On Proton, the game usually fluctuates ~25 FPS but it's possible to run it through an RPG Maker MV / MZ Linux wrapper for performance that's much more comparable to Windows.

• Install the RPG Maker Linux wrapper: Follow the instructions from here or run wget -qO- "https://raw.githubusercontent.com/bakustarver/rpgmakermlinux-cicpoffs/main/installgithub.sh" | bash
• Run rpgmaker-linux --steamskipgui
  • If rpgmaker-linux isn't found, restart or go in and out of Gaming Mode
• Go to /home/deck/desktopapps/nwjs/nwjs/packagefiles and edit package.json: Make a new line after line 10 and add "fullscreen": true,
• In your Steam library, go to F&H2 -> Properties -> Compatibility, check "Force the use of a specific Steam Play compatibility tool" and choose "RPG Maker MV/MZ (clcpoffs mount) Tool

The game should now run properly in Gaming Mode at ~60 FPS. This fix can also be used for other RPG Maker games, just change the compaibility tool to RPG Maker MV/MZ Tool for whatever game you want to use it on. To fix minor frame stutters you can try some of the Windows-specific fixes as those are RPG Maker quirks (nwjs upgrade is unnecessary because the wrapper already uses a much newer nwjs version)