Is there an alternative of CS 1.6 that runs on Linux and newer MacOSs and doesn't need a quantum computer run (I mean relatively moderate specs :))? I think CS:GO was made unnecessarily heavy without any substantial improvements over 1.6.

I also liked Project IGI - simple mission game. I am not into gaming really. Sniper Elite is like this by any chance?

These were the only games I liked and I'd like to try something like that again. I like normal/realistic game plays - no extra/exotic powers or sci-fi cartoonish elements to a game.