Tentaphage is compatible with Steam Deck using Proton! Tentaphage should run by default using the "Ultra" settings, but seems to run best using the "High" settings.
"Medium" still looks okay and is best suited for limited battery.
"Low" is not recommended and only needed for very low performing PCs.
Steam Input images are not included in the game, but all inputs work properly using the standard "Gamepad" configuration.
Steam Input works properly with Tentaphage.
Tentaphage Steam Deck Compatability
Source: Steam Community (opens in a new tab)