Linux app can't sign in

Summary
Once I sign in with SSO (via Gitlab) in browser, no prompt appear to open the app and so it can’t receive the token and stays in the “awaiting token” page forever.

Steps to reproduce
Use:
Mattermost Linux tarball : mattermost-desktop-5.10.2-linux-x64
(but same on all the options, including the official tarball and the unofficial AppImage and unofficial RPM too)
Chrome : 132, same with Firefox 134.0
OS : Fedora 41 Workstation Kernel : Linux 6.12.9-200.fc41.x86_64
Gnome 47 on Wayland

Expected behavior
A prompt to launch/open Mattermost desktop appears in the browser, once clicked on Open, Matermost is logged in and can be used.

Observed behavior
No prompt appears in the browser to open the app and so it can’t receive the token and stays in the “awaiting token” page forever. It’s possible the app isn’t ‘registering’ an URL handler for mattermost:// URLs, which should redirect and open the desktop app.
Is it there a manual workaround I can try?

Note that Zoom.us uses the same SSO sign in method, and it works perfectly.