aquired galaxy installer (GOG’s site hides download links on linux… why???)
proton gog-galaxy-installer.exe to install. It installs to ~/.local/share/proton-pfx/0/pfx/drive_c/Program Files/GOG Galaxy (or somesuch)
I made a shortcut to launch the galaxy.exe with proton from the directory & using the directory as working directory
profit.
Seems to work fine, some older version of proton-ge and/or nvidia driver under wayland made the client bit sluggish, but that has fixed itself. Games like Cyberpunk work fine. The galaxy overlay doesn’t, though.