Our community member Xtek manage to solve this by using some convoluted dark magic ;).
- Steam Version of Heroes of Might & Magic V: Tribes of the East
- Heroes 5.5 installed on PC with Windows
- Having a PC with Ubuntu 19.04
Steps to configure:
- Install Steam on the Ubuntu PC
- Navigate to "Steam>Settings>Steam Play" and Enable the "Enable Steam Play for all other titles" option.
- Select the latest Proton version (at the time of this post 4.2.4) for the "Run other titles with:" option. Press ok.
- Right-click the Heroes of Might and Magic V: Tribes of the East game link on the left side of the library panel. Press the "Set Launch Options..." button and paste this in without the quotes: "PROT %command%". This step will smooth out FPS in the Main Menu.
- Now on the Windows PC - Navigate to the Heroes 5.5 folder you have installed and copy ALL files to a USB drive.
- Back to Ubuntu PC - find the game's install folder by right-clicking the game in Steam and navigating to "Properties>Local Files" and then clicking the "Browse Local Files" button. Paste ALL of the files from the USB drive to the game installation folder and make sure to MERGE all the folders and to OVERWRITE EVERYTHING. You can make this step simpler if you have direct access to the Windows folder via Ubuntu's file manager by copying everything directly without the need for a USB drive.
- Switch the names of the "H5_Game.exe" and "MMH55_64.exe" located in the "bin" folder of the game's installation folder. This step will enable you to run 5.5 directly from Steam, automatically running it via Proton and applying the fix #1 (step 4).
- This is the Fix #2 that should be applied everytime you launch the game. Starting a game will have a terrible FPS so to fix this open the "Options" and go to "Video and Audio" section. There select the "Anti-Aliasing" bar, change the value and hit "Apply". That should instantly fix the FPS. You can also change the setting back to the value you had before and hit "Apply" again, and the FPS should still be fine. Even if you start another match, the FPS should stay fine until the game is not closed.
- You are ready to play!