System Information
Retest Compatibility Report
Game runs now without needing launch option "-onethread". Remaining issue is that videos are skipped (I have tested that installing Microsoft Media Foundation does fix that).
Re-Test Report
Game works now without issues out of the box including video playback. Except on Intel 10th gen+ CPU's because of OpenSSL bug. This is another UE4 game affected by this OpenSSL bug: https://github.com/ValveSoftware/Proton/issues/5830
I was able to play this game without problems setting Steam Launch option:
"OPENSSL_ia32cap=0x20000000 %command%"
Closing this issue as I'm no longer seeing any Proton/game specific problems. Logs for future reference:
steam-1029890.log
system_info.txt

^ Screenshot of working video
Finished the game with Proton 7.0-5 on Steam Deck. Every video works except the final one for formless ending (didn't get to testing other endings). Instead the game will froze and you need to forcefully shut it down.
With Proton 7.0-4 this happened on the first video you encounter in the game.
proton 7.0-4x1 2022-11proton 7.0-5x1 2022-11proton 7.0-3x1 2022-06proton 4.11-6x1 2019-10OPENSSL_ia32cap=0x20000000 %command%x1 2022-06mfplat.dllx1 2019-05
Compatibility Report
System Information
I confirm:
Symptoms
Out of the box game crashes on launch (included logs of that happening with different Proton versions). Setting Steam launch option "-onethread" you can get into gameplay, but the videos/cut-scenes are skipped/do not display.
media_info.txt
steam-1029890_proton-3.7-8.log
steam-1029890_proton-3.16-9.log
steam-1029890_proton-4.2-5.log
steam-1029890_proton-4.2-5-onethread.log
#1464 I see mentions about mfplat.dll in the logs, videos are: MPEG-4, AVC + AAC
The subtitles are not embedded but in separate .srt files.
Reproduction
Just launch the game.