For native Steam installations (most common):
~/.steam/steam/compatibilitytools.d/
For Flatpak Steam installations:
~/.var/app/com.valvesoftware.Steam/data/Steam/compatibilitytools.d/
Download the latest GE-Proton release: Go to the official GloriousEggroll GitHub https://github.com/GloriousEggroll/proton-ge-custom
Extract the downloaded GE-Proton10-10.tar.gz file directly into the compatibilitytools.d folder. Make sure the extracted folder (e.g., GE-ProtonX-XX) is directly inside compatibilitytools.d.
Make sure to unzip the achieved file GE-Proton10-10.tar.gz and removed the archived file after extracting all the folder contents
Restart Steam: Close and relaunch your Steam client.
In Steam go to "Compatibility" tab and choose the GE-ProtonX-XX and it will prompt you to restart the Steam again to take effect the changes.