Which product do I use to treat garage walls that " sweat "in the winter

You don't need waterproofing, you need insulation.

Unless your garage is underground, "sweating" is actually condensation, and it's due to the walls being cooler than the air, and below the dew point. One way to prevent it is to dry the air, but dehumidifiers consume energy (= cost money) to run, and chemical air driers cost even more over any significant time period.

The better way to prevent this problem is to ensure that the interior wall surface doesn't get below the dew point, by keeping it close to the inside air temperature -- and the way to do this is to insulate. Reduce the rate at which heat is lost through the walls, and the warm, moist air (presumably infiltrating from the heated house) won't have a place to deposit moisture.

This isn't a super-easy DIY job, unless you're the sort who could build the garage in the first place -- but if it can be done from inside (by removing drywall) instead of from outside (removing siding, vapor barrier, etc.) it's not terribly difficult, especially if you don't mind seeing joints and nails or screws in the inside dry wall.

The inexpensive product (in my experience, which is pretty old, so check behind me on this) is "rock wool" or fiberglass insulation batting, and a recommended R value for an unheated garage is fairly low -- R-14, perhaps, to R-18 -- but if the garage is connected to the central heating, it should have been insulated when built, and the recommended values today are something like R-24 to R-32 (again, check me, I'm neither a contractor nor a young fellow and these values tend to rise with time as energy costs and environmental concerns rise).

You have this on lifehacks and not DIY,SE so if you want a simple and low cost hack, try leaving the door open.

This will create airflow which should help stop/reduce the condensation.

Downside is that leaves, snow, stray cats, burglers, lost children, birds, bugs, litter/garbage, dust, dirt, and confused moths could all end up inside your garage over time. This may make a mess and subtract from the utility of the life-hack solution.

If its your own property, do it right as per the answer from Zeiss. If its a rental, advise the landlord/management.

Clean the floor.

Wet Warehouse Floors in Atlanta – southeastsealing.com/wet-concrete-floors

As this moisture vapor migrates to the surface of the concrete floor it carries with it mineral salts and other impurities within the concrete slab. When the moisture evaporates, the impurities are left on the surface and result in a white colored residue known as efflorescence. Unfortunately, this is not just a cosmetic problem.

Efflorescence, or salt deposits are hygroscopic in nature. Consequently, they absorb and hold on to moisture in the air. Thus, a lack of a vapor barrier can significantly contribute to wet concrete floors and sweaty slab syndrome. Routine cleaning of the floor with a floor scrubber using water and detergent can help remove efflorescence and reduce moisture accumulation.