I use Gog Galaxy for a few months now, maybe longer, and don't get any problem with it since today.
Today, I can't launch Crusader Kings 3 from Xbox (play button is greyed) but others Xbox games can (AoE2, AoE, Forza 7 all 3 works fine)
Yesterday I could launch it just fine.

Edit : Forget that I can launch it today, the button is not greyed out anymore.
I don't know what was the cause but I had to reboot my pc.