Choosing a gravel
A mountain bike is not a universal soldier and is not suitable for most reels. Let's divide the entire market into several segments: classic city bikes (here we include grandfather's "adult", and all kinds of cruisers there); road bikes (we also include dressing and triathlon bikes - all this, whatever one may say, is primarily sports equipment); mountaineers (Niners / non-Niners - they are all for one profile). There remains an expanding segment of the so-called hybrids and other touring, and here the bicycle industry suddenly threw a novelty into the masses.
They are still deciding there how to call it all correctly and uniformly, but in our market, such bicycles are classified as gravel bikes. From the outside, they can be inadvertently confused with road bikes (and indeed, some of the advantages of this class have been adopted), but the gravel is an independent unit. It is slower than a road bike, as it does not have such a sporty geometry, but this is what makes it feel more comfortable on it. Pros can take seven hours straight in the saddle in an uncomfortable position, but you may not need it. In addition, gravels are equipped with more versatile rubber: wide (usually up to 38 mm or even more), with a sane tread. Such tires roll with dignity on the asphalt, while easily swallowing any non-extreme off-road.
Frame material
The price is another matter. Gravel will certainly be more expensive than rivals in the same class. Its cost tends to be the price of a road bike, which is understandable given the similarity of the components.
Let's start with the frame. You can find various options on the market, but you will most likely have to choose from aluminum and carbon. The fact is that steel, although loved by connoisseurs of the classic bicycle image, is gradually receding into the shadows and is increasingly being used except by boutique brands. A boutique brand is when it is completely unclear why a product costs so much. Adepts will object: the point is that only the most expensive materials are used in production. But this does not change the question - why? We're still talking about bicycles, right?
Around the same place, you have to push the titanium frames. They are good for everyone: titanium is light and at the same time strong (it is difficult to even scratch it), does not corrode. But it is rare, expensive, often exclusive. In short, if you want a titanium frame - our compliments to you. Well, if there is no urgent need, it may make sense to choose something more accessible.
In this sense, the most affordable material is aluminum. And the truth is, it's good for everyone: lightweight, durable, durable. It does not rust and is almost never out of date. Aluminum is good for making aircraft, and trust me, it's good for making bicycles. But it's affordable and inexpensive, which is why marketers often turn up their noses - don't listen to them.

The second option, without a doubt (we can say the choice of professionals) is carbon. We have already talked about how it can be good and bad, expensive and not very expensive. The main advantage of carbon fiber is its rigidity and at the same time the ability to absorb vibrations. The stiffness of the bike is the transformation of your efforts in motion: the stiffer the bike, the less energy is wasted. But you also need comfort, otherwise, the road surface will shake your whole soul out of you. Carbon will give you more comfort than aluminum.
But there are also disadvantages. First, the merits of cheap carbon remain a matter of controversy. Correct weaving of fibers, the number of layers, the raw materials used - all this is a rather complicated science. It's a shame to overpay and not really get anything for it. For example, a lousy carbon frame won't be any lighter than a good aluminum frame, but it will definitely sell for a lot more in marketers. Secondly, carbon is material, although reliable, but not quite shock-resistant. It will withstand the rider and almost certainly will not break even on difficult terrain, however, an unsuccessfully bounced pebble off the road can easily leave a noticeable chip. And gravel, we understand, is not a bicycle for parquet.
In general, you need to choose a frame with an eye on the budget. In any case, we have the right to expect that our gravel will weigh in the region of 10 kg, or even less, which is very good for a bike of such cross-country ability. Weight and speed, we remember, he inherited from the road bike.
Why bent steering wheel?
What else gravel inherits from a road bike is a ram handlebar. Some people look at it skeptically, preferring a direct flat bar or riser. And completely in vain. There are undeniable advantages to a road handlebar. It's at least the right width: 70cm handlebars make sense on tricky trails where steering is a factor, but on less specific rides, you will find it much more comfortable to ride with your arms outstretched shoulder-width apart, rather than trying to cover a ball in the gym. But the most important advantage of the "ram" is the variation of the grip. Moving your hands, grabbing the steering wheel from below, from above, by the handles - all this is an opportunity to relieve muscles, prevent painful sensations during long trips. In general, try it by all means: add to the taste - it will not be pulled by the ears, that's for sure.

Another important point is the stem, namely its length and height. Feel free to experiment with this: the steering column of the bike is made in such a way that the stem can be rearranged higher or lower, and besides, it is not a problem to find a model that is longer or shorter. Also, adjust the saddle position, find the best fit for you, and long bike rides will no longer be a problem.
Brakes
When it comes to bikes that are used off-road, bicycle disc brakes are considered the best choice by default. There is one more nuance in the case of gravel stones. Attachments to this type of bicycle are largely inherited from the highway branch of bicycle construction. Not so long ago, in particular, Shimano and Campagnolo released specific classes of equipment manufacturers: GRX and Ekar, respectively. But road calipers cannot be used on gravels - the tires are too wide. Cantilever brakes solved the problem but did not receive proper technical development. So your gravel will have disc brakes, period, no alternative. Well, okay, in this case, the discs really fit organically into the overall concept of the bike.
Another thing is which brakes to choose. There are two options. The first, budgetary, is disc mechanics. That is, the brake pads are driven by a metal cable. Such a mechanism is very easy to maintain and configure, moderately reliable, and, as a rule, inexpensive to operate. There are also nuances: in some models, for example, only one pad moves, pressing the disc against the other. In any case, the bike will slow down, but such a mechanism is far from ideal.
Hydraulic disc brakes are something that came to cycling from other, heavy modes of transport. Such a braking system is the most modern, technically complex, but at the same time effective. The bicycle brake pads are compressed by the hydraulic fluid. There is no need to be afraid that at the wrong moment the hydraulic line will break - all these are horror stories for fans of this genre. Nothing will happen to the hydraulics, rather the block will jam if the brakes are not serviced, at least from time to time, but this is a risk for any technology. Therefore, the choice is obvious for many, everything again comes down to the possibilities of the budget.
If we compare with other classes of bicycles, then in any mountain models rims have taken root for a very long time, and road cycling literally in two or three years has also almost completely switched to this side. And if in the case of road bikes everything is not so simple (the problem of overheating, disgusting squealing has not disappeared anywhere, and in general, many consider this technology redundant for the highway), then for travelers, discs are flesh of flesh. For the off-road, nothing has been invented more reliable than disks, and issues with overheating and other "sores" identified on high-speed highway descents simply do not exist in another genre - the wrong speeds.

Number of stars
Another know-how that marketers have tried unsuccessfully to sell to road cycling is one star in the front, which is a single-speed system. Wrong: the speed range is too wide and varies too much depending on the terrain. But for the gravel, everything is completely different. Having one star in front means narrowing your choice to some extent. But it will still be sufficient: it is difficult to imagine a situation when a set of 42 or even 44 in front and 11-42 in the back will not be enough for both a beginner and an advanced cyclist. Plus, the simplicity of the design will make you happy: save on the front derailleur.
If you intend to chase in earnest, changing the type of coverage from asphalt to off-road, then you can pay attention to bicycles with two-speed systems. Traditionally, in such models, the stars are set at 46-36 in front, which closes the issue with the gear ratio on any terrain.
Although the general trend for the view is fewer stars in the front and more stars in the back. 13-speed cassettes are no longer uncommon, but unlike other types of systems, the number of stars in the back does not affect the bike's rigging in any way.

Cyclocross affinity
Well, a few words about what the frame geometry affects. Gravel is a bike for everyone because it was not created as purely sports equipment. Take a road bike: a low and extended landing is initially assumed to achieve the best power and speed characteristics of the rider. As a result, the poor fellow sits hunched over in three deaths, not even being able to raise his head normally.
The masses do not want that, the masses will not go that way. Therefore, in gravels, the frame geometry is shortened, which allows you to sit straighter and higher, that is, more comfortable.
Manufacturers in this sense are at a crossroads. Few people from scratch began to develop gravel for their own lineup. Creating a bicycle is not an easy process, and the result is always uncertain: whether a new product will enter or not, what, in principle, will be the trends in this direction. Realizing this, the industry took a different path. Whoever had something successful in the lineup tried to adapt it. For example, the famous bicycle brand takes a successful model of a road bike. Shortens frame and widens clearances to accommodate wide wheels - gravel. The other had a good cyclocross. Through light processing, the same gravel is obtained from cyclocross - it is conveniently the same. The main thing is to come up with a name for adventure and endurance.
By the way, a few words about cyclocross. Those who are more experienced probably raised an eyebrow critically from the very beginning of the conversation, having noticed some clear similarities between the two types of bicycles. Relax, gravel - it is simpler, more accessible. Cyclocross, like the road bike, remains a highly specialized sports equipment with the corresponding ruthless requirements for the athlete in terms of training (including landing). But if you have some experience behind you, you can take a closer look at cyclocross - there are indeed many similarities.