Eh, I don’t really think that this is an “or” situation. I think that this is an “and” situation. The last time that I set up Xash3D FWGS, I had to copy files from the version of Half-Life that I own on Steam into a different folder so that those files could be loaded by Xash 3D FWGS. I haven’t tried Xash 3D FWGS in a while, but it looks like you still have to do that [1]. Also, are you sure that the Steam version of Half-Life is Windows only?

[1]: <https://github.com/FWGS/xash3d-fwgs/blob/f0342763547d9bcf486...>