Totally missed that part. That is nuts. Thanks

How does this differ from a forced Microsoft login in eg. Forza Horizon 4 or Halo?

Forza Horizon 4 currently

I tried the Epic Version of BL3 (when they gave it away) via Heroic Launcher and that works flawlessly. However I did not yet try online coop.

This is the correct thing to do when it breaks, recompile and link against the new libs. Otherwise you could see funny behaviour.

It has Steamdeck Support with the same Deck UI as on the official SteamOS.

Had the same issue, but it solved itself somehow. Now I am too afraid to look into it, in fear of triggering it again :D

I am playing my epic games exclusively via heroic and it is a blast.

Played it for the first time some weeks ago. It was like playing Half-Life 2 for the first time again. Loved it.

Magic Arena is nowadays on Steam and it works quite painless via Proton