You can see our gameplay and video guide for the best settings so far, but it's far from a completely stable 30 FPS at this time, but it does show a lot of promise and the dedication of Valve to get games working on the Steam Deck
UPDATE: As per the news article here https://www.steamdeckgaming.net/post/steam-os-3-4-6-update-released
You no longer need the preview channel as specified below.
First off, to play the Resident Evil 4 Chainsaw Demo on Steam Deck, you will need to head over to the System Updates and switch over to the Preview channel
You will also need to make sure you have all of the latest updates and ensure Proton Hotfix is also up to date. At the time of writing this article, the demo was not working properly in the Beta or Stable branches, only preview.