One thing that you need to do is to use Heroic Launcher downloaded directly from their website instead of using Discover Store (flatpack). It will be saved as an AppImage application, I used AppImageLauncher to install it on steamdeck desktop mode.

Then just simply add heroic into Steam as non-steam "game" and run. Remember to add WINEDLLOVERRIDES variable.

If you want to use cheats/mods you can install it manually and then add mod dll name to WINEDLLOVERRIDES after vulkan-1 by coma, for instance, WINEDLLOVERRIDES=vulkan-1,mod_file.dll=n,b