While the full 2023 remaster is a paid product, there are several ways to play portions or specific versions for free:
Enemies now have better pathfinding and new behaviors. quake-2-pc-game-free-download-full-version
For a few dollars, the Quake II Remaster (released in 2023) is widely considered the "definitive" version. While the full 2023 remaster is a paid
If you are running the original files (not the remaster), you will likely need a to make the game work on Windows 10 or 11: quake-2-pc-game-free-download-full-version