Apparently this issue has already been reported earlier here: Game not starting at all (latest update) - #6 by TheTugaTog
For Linux in specific, the newest Proton Experimental does indeed fix the issue on my end.
Reddit info: https:// www.reddit. com/r/aoe2/comments/14mwbz2/aoe2de_playable_again_on_linux_via_steamproton/
Issue tracker: Age of Empires II: Definitive Edition (813780) · Issue #3189 · ValveSoftware/Proton · GitHub
Sorry for the link breakage. New users may only have 2 per post for whatever reason.