Edited some registry settings to lower mouse sensitivity and game resolution according to this guide (https://steamcommunity.com/sharedfiles/filedetails/?id=3174952613), although the effect was rather minor.

Dungeon Keeper 2 works perfectly with Proton, with a couple of small gotchas:

• A Proton version based on Proton 9.0 or higher, such as Proton 9.0 (Beta), Proton Experimental (currenty based on Proton 9.0), GE-Proton9-1, etc. This is required to fix the game running at 11-14fps (tested with GameScope which shows the Steam Overlay, and the Steam Overlay reports this framerate). Once selected the game runs buttery smooth.
• This one seems not to be related directly to Proton, however, the game mouse sensitivity and scroll sensitivity, even with the lowest possible registry settings, are still way too fast for my tastes. I have not found a way to fix this, but I wanted to note it as issues like this are sometimes Proton-specific, but for Dungeon Keeper 2, it appears to not be Proton-specific.
  • See this forum thread for the GOG version voicing a similar complaint (the Steam release is the same as the GOG release as far as I can tell): https://www.gog.com/forum/dungeon_keeper_series/dk2_mouse_key_movement_sensitivity_way_too_high

Overall works great once I changed the Proton version, although has a couple of small control QoL issues simply due to the game's age. Tested on KDE Plasma Wayland 6.0.1.