I think it’s a fairly standard feature. At least Protonmail also supports this kind of “alias”.

I think this should work assuming that the game and mods are compatible with proton. Also, you don’t need an external drive, you can access the windows partition from linux (probably not the other way around though since linux understands NTFS but windows doesn’t understand ext4). If there are any issues, maybe try the “Verify Game Files” feature of steam. This might remove the mods but at least you don’t have to download the game again.