This issue still happens with Proton 4.11-10, and I can't fix it with mfplay.dll as @Gravemind reports. Game is still running on background as the hint sound plays after a while, and the whole game is perfectly playable ...
Like many other games, requires mfplay.dll (etc...?) for the cutscenes to play. Without MF, the game freezes at cutscenes and this is a game breaker. With MF, proton 4.11-9, nvidia, everything runs great.
Issue still exists using Proton 4.2-9 The problem with the broken cutscene is that it prevents you from doing the alternative endings because you don't get the chance to go back redo the end. So it would be really nice t...