Running a steam game without steam doesn't work

Here's my scenario: I've just modded Baldur's Gate 3 and it works. There is an update coming soon that will break my modded installation. When this happens, I want to play the game without updating. This means I need to launch it outside of Steam. On Windows I can do this by clicking the exe in my game folder.

On Linux this isn't working. When I click it, Protontricks opens and asks me what Wine prefix to run. I have one called 'Baldur's Gate 3' and several others for other games. Choosing any of them does not work, the game just doesn't start.

On the other hand, I can launch it from Steam. In the game settings > Compatibility section, its using Proton Hotfix. There is also a launcher argument needed to make mods work:

WINEDLLOVERRIDES="dinput8=n,b" %command%

I don't quite know what Steam does when I tell it to launch the game, but it seems to be doing more than just running it out of the local folder. So my question is - How can I sort of 'recreate' this behavior outside of Steam, once I'm no longer able to use Steam to launch the game?