As of yesterday (10 May), I also had this issue on my work machine. Needed to restart the machine (Mattermost working perfectly normally), and on restart, the program would boot without a window. Deleted and reinstalled (App Store version), same issue. I’ve got it up and working with the GitHub version, but it’s definitely an issue that it won’t update from that file.
ETA: @agriesser I went looking for the logs, and I can’t see the Containers folder that is specified by the file path in the docs. I can get to the Library, so either that file is hidden to my access level or it’s not being created by the broken version. But whatever it is persists after it breaks and only applies to the App Store version. I went back and reinstalled the App Store version after successfully signing in to the GitHub version. It overwrote the application, and when I quit and reopened, the issue reappeared.
Tried to recreate on my personal machines, but both my 2013 iMac and my M2 Air load the program fine on install and after restart.