Hello @hackcr1258, this reads more like an abuse of the flexibility left into Steam's launch options more than a Proton issue. %command% gets replaced with the command Steam uses to start the game, so I read your tinkering as run an arbitrary .exe (with system wine?) with a pile of ignored arguments after it which would have been starting up Proton.
This approach isn't something that can be supported from Proton's side.
Compatibility Report
System Information
I confirm:
P.S.: I could not get a log no matter where I place PROTON_LOG=1 within any part of the command in reproduction
Symptoms
Using a custom launch flag to skip the launcher results in the game not recognizing the steam client.
Reproduction
"~/.local/share/Steam/steamapps/common/Zenless Zone Zero/games/ZenlessZoneZero Game/ZenlessZoneZero.exe" %command%as launch arguments.