On itch.io (https://itch.io, https://github.com/itchio/itch, MIT) you can find a lot of Linux games. The best thing is, the itch.io app is completely open source! Not like GOG or Steam, itch.io is extraordinary in this regard.
You can install the itch.io client from AUR (https://aur.archlinux.org/packages/itch):
Or the development version
Itch/kitch doesn’t work on Wayland (Bug) only trough XWayland. With itch 24 they switched from Gtk2 to Gtk3 to make it work on Wayland, but at the moment is still works only through XWayland as the Electron toolkit must switch to Gtk as well (https://github.com/electron/electron/issues/2927).