Often on sale for a few dollars, the Return to Castle Wolfenstein Steam page includes the single-player campaign and is compatible with modern Windows.
The most popular source port. It improves performance and stability on Windows 10/11.
Install the game via Steam or GOG, then download the ioRtCW files from GitHub and place them in your game folder.
Offers a DRM-free version that is often pre-patched to run better on modern systems.