Nice old stutzen, with what seems to be a lovely walnut stock that would benefit from some careful cleaning.
Rifles marked BRNO were produced in Czechoslovakia beginning soon after WWII. A number of manufacturers were included, and the government required any designed for export (many going to West Germany) had to carry the BRNO marking. With the fall of the Soviet Union, the manufacturers became independent and CZ began exporting under its own name.
This particular rifle with the Bavarian cheekpiece was clearly intended for the German market. The side mount is somewhat unusual and closely resembles a model used by the Wehrmacht on sniper rifles during the war. Judging by the scope, this rifle was probably built in the sixties and I would agree that it is likely a M21 or M22 - I do not have my reference books handy.
It is marked that it is chambered in 8x57S, which was the standard military 8mm chambering and uses a .323 bullet rather than the .318. It is an excellent general purpose chambering roughly equivalent as the 30-06.
The rifle has a classic, if often finnicky, double set trigger. If you pull the rear trigger first, it will set the front trigger to fire with a few ounces of pressure. Pulling the front trigger first should provide a trigger pull of around three or four pounds.
I doubt the scope is fog proof, but if it works, use it. Trying to fit another scope onto that mount would have to be done by an expert and and the costs would be more than the value of the rifle. Assuming it is still an S bore 8mm, always verify with a chamber cast, these rifles are priced typically at gun shows 800 to 1200 USD.