The base system draws from Debian 8, code named Debian Jessie.
Most/many Windows-based games run on SteamOS and other more general Linux distributions via Proton, a largely Valve-developed fork of Wine that's integrated into and supplied with Steam for Linux. Note that also the Steam Deck uses SteamOS. The biggest trouble spot is Windows games using anti-cheat, of course especially kernel-level, and some forms of third-party DRM. There's a general compatibility database at
https://www.protondb.com/explore
Linux has mostly what windows has Firefox or other programmes are available on Linux, it is nowadays no problem to use Linux for normal use windows is not needed any more.