Has anyone tested the game on a steam deck? Will the game run and access the on screen keyboard and other functions? Do you have to do anything special during the install?

download the windows version .exe, then just use proton works just fine. or dual boot with windows

Your suggestion worked. For future reference, I downloaded the installation exe and added it as a non-steam "game" on steam (launch steam from desktop mode) and set the properties to use proton. That ran the installer and created the vendetta folder in the /.local/steam/steamapps folder. Repeat the process of adding a non steam game for the vendetta exe and voila.

The only thing that would be required to make vendetta to work on the
Steam Deck / SteamOS is to use support GTK3 (installed by default on the deck)
Instead of the GTK2 (not installed by default and requires sudo modification to the os)
In the install script and probably the games code.

For posterity I'm linking this to the more recent Steam Deck testing thread. We do have preliminary support, although still a bit "beta" stage.

Also, fyi that adding support wasn't trivial: it required a lot more than just a gtk update. The Deck only makes its controllers available in a particular "mode", and there was quite a bit of work required to make the game function smoothly and detect the device, and so on.