I downloaded the files mentioned by others and pasting them to "/PartyHard2Game_Data/StreamingAssets/low_quality_cutscenes" did nothing.

However, I pasted them to "/StreamingAssets/cutscenes" instead and so far everything works perfectly fine.

Alternatively, the cutscenes worked pretty well out of the box in Proton-6.12-GE-1, but the overall performance of the game has degraded.