They are all over the place, actually. For example Audi/VW uses two different types of AWD system: quattro and haldex. Rule of thumb, if the engine is mounted longitudinally it will have quattro; if it’s transversal, haldex. Quattro has a center differential that by default will split the torque in some way, for example 40/60 or 50/50 or whatever, but it can send more to the front or rear as needed. Haldex by default sends all the torque to the front, and as soon as it senses that the wheels are slipping, it starts to send some torque to the rear, and it stops doing that as soon as it senses that the front wheels stopped slipping.
Subaru also uses several different types. There are videos on youtube where they explain the 4 or 5 different systems used by Subaru. The only ones I remember are thr WRX uses a mechanical center diff that always splits 50/50, and they use the brakes to transfer torque to the wheels that are not slipping. The WRX STi on the other hand, very different. It has a center diff where the driver can actually dial in the split, or be automatically controlled, plus the front and rear diffs are torsen (the front and rear diffs on the plain WRX are open).
I don’t know what Mercedes does but fuck Mercedes.
Most tires that are rated for deep snow (three peak symbol) are dedicated winter tires, but there are some all-purpose tires that also have the three peaks. I used to have a set of Yokohama something or other that were all-terrain and deep snow rates, and I used that car in the snow and the tires performed pretty well. Now I have a set of BF Goodrich all-terrain which also have the three peaks, and I also drove in deep snow and they were fine. All-terrain tires with the three peaks can stop a lot faster than regular “all season” whatever tires, but they are not as good as proper winter tires.