Until such a time as Fullbright Presents TOILET SPIDERS makes its way through the official Steam Deck verification queue, here's the state of the state: as far as I know, FPTS should be fully Steam Deck compatible, and meets all requirements for Verified status!
The game makes use of the Steam Deck's gamepad controls by default when launched on Steam Deck, and displays Steam Deck button names, not keyboard binds. The game runs at 60fps on default settings, with some areas that may dip more into the 55fps realm. Currently you can't manually adjust the screen res, but in a future update you should be able to bump down the screen res to lower than native res if you really want to maximize framerate on Deck (maybe I'll find some general performance tweaks in the future as well.)
Steam Deck: anywhere you go, there's Toilet Spiders!