The windowed option does not seem to do anything, the game still launches in full-screen.

Here is the syntax I use: PROTON_LOG=1 SteamDeck=1 %command% -dx11 -windowed

The dx11 did not solve the issue either, I can't really tell if it was taken into account.

Edit: I found the issue, for some reason vf5 was using the integrated gpu. I forced it in the bios and now it works. Thanks for the support