DOOM + DOOM II adds multiplayer mod support but it's broken on Steam Deck / Linux

Update 29/01/25 - 18:42 UTC - An update has been released that appears to have already solved the issue. Nice to see such a quick turnaround direct from the developer on this one!

Original article below:

The updated version of DOOM + DOOM II that bundles them together with enhancements from id Software / Nightdive Studios, Bethesda just got Update #2 with more improvements for playing with mods.

With this new update they've added support for mods during online play. They say game hosts need to activate it before entering the multiplayer menu, with other players needing to subscribe to the mod before joining a match. Mods for the game collection must be made with either "Vanilla DOOM, DeHackEd, MBF21 or BOOM" to be compatible.

Various other changes also came with the update including:

General

• Resolved an issue in which some red doors did not display as red on the automap
• Fixed multiple crashes reported by the community when loading game saves
• Improved text line wrapping legibility for mod descriptions in Asian languages
• Removed map prefix from intermission screen to be consistent with original game behavior

Multiplayer

• Added spectator mode when players are dead and waiting to respawn in co-op mission play (it can also be initiated manually from the scoreboard button)
• Fixed an issue in which disabling the crosshair would also turn off player name and co-op respawn text display
• There are now more than 4 player colors available in game and on scoreboards
• Resolved an issue in which players would lose weapons when respawning in co-op using modern rules
• Fixed an issue in which the cross-platform friends menu could not be properly backed out of when no friends were available
• Further optimized multiplayer networking code
• Addressed crosshair centering issue in certain splitscreen configurations
• Intermission animations now run at the correct speed in splitscreen mode

Modsl

• The mod downloader can now process more than the first 100 subscribed mods

However, there's also reports that it has been broken on Steam Deck. Causing the developer to add the previous update as a Steam Beta (no password) and edit their update announcement for anyone affected while they work on a solution.

Initially I got a bit confused, because both singleplayer and online play worked fine on both Desktop Linux and Steam Deck. But it's specifically playing with mods that causes the problem. As soon as you've got even a single mod downloaded, the game will no longer run and leads to this error:

I've noted it in the Proton GitHub bug report with log files from both systems, so hopefully Valve developers can track down the issue in Proton.