Portal Stories: MEL is a free total conversion of the Portal game with a whole new story and content. Your character is thrust into a huge salt-mine in the early 1940s and put to sleep in a chamber. Then you are rudely awakened with the world around you crumbling. Use a new portal gun to find your way through epic underground testing facilities.

https://store.steampowered.com/app/317400/Portal_Stories_Mel/



Portal Stories: MEL is fully ported to Linux and ran fine on my GeForce GTX 1060. I never had any performance problems and didn't even need Portal 2 installed in Steam. So this is a stand-alone version.

Specs:
Mint 20.1 64-bit
GeForce GTX 1060
Nvidia 460