Black screen in several RPGMaker games

Compatibility Report

• Name of the game with compatibility issues: Princess Project (one example, some others as well)
• Steam AppID of the game: 1106080
• See workaround at end.

System Information

• GPU: Radeon Vega 56
• Driver/LLVM version: Mesa 20.0.2
• Kernel version: 5.5.13
• Link to full system information report as Gist:
• Proton version: 5.0-5

I confirm:

• that I haven't found an existing compatibility report for this game.
• that I have checked whether there are updates for my system available.

Symptoms

Black screen in several games, audio from title playing so game is otherwise working

Reproduction

Starting the game.

Workaround

Seems to happen in games using ffmpegsumo.dll.
Upgrading from nwjs (https://nwjs.io) to 0.44.5 with actual ffmpeg.dll fixes problem and game starts correctly.

Questions remaining

Is it enough to work around that single DLL? Or are the other files also absolutely necessary (is it enough to detect just that DLL?)?
Is it possible to have Wine detect this or to include workaround or is the game update always needed?

Start with the compatibility report for Princess Project (Steam AppID 1106080) and reproduce the black screen when launching it under Proton 5.0-5. Compare the behavior with NW.js 0.44.5 and the reported ffmpeg.dll workaround, then determine whether the issue can be narrowed to ffmpegsumo.dll or requires broader game or Proton changes.