I had also heard that at some point they were being directed to adapt the idTech engine which runs DOOM to become the new base for Bethesda games, but I guess that hasn’t happened.
They must have had trouble, because Arkane moved from Unreal to Void (which is built on idTech) for Dishonored 2 and Deathloop and such, and then back to Unreal again. Everyone got in a hurry in the 2010s to have their own in-house engine to avoid paying out fees to Epic, and then after running into trouble trying to adapt those engines to genres they weren't built for, they're back to Unreal again.