There used to be a way to run Proton outside of Steam but i think it is now discouraged.
There used to be a way to run Proton outside of Steam but i think it is now discouraged.
1. Download gog install files into the same directory
2. Add the install executable as a non-steam game, and enable proton compatibility before starting it up.
3. Run the installer and complete the installation. Gog installers typically give the option to run the game from the installer, but that will only work once.
4. Find the path of the installed game, and the working directory of that executable by searching in ~/.steam
5. Edit the entry created from 2. with this exec path and working dir, and look up possible args from protondb.com
It's how I run my GOG games on Pop OS.
TBH i do not think things are completely unsolvable, it is just that i wish Proton, etc wasn't tied to Steam.