The TL;DR: The game won’t launch on current steamOS, but preview build 3.7.6 fixes the launch issue.
Unfortunately the game is unable to maintain decent frame rates even with severe reductions in graphical settings.
The drastic decrease in performance compared to Doom 2016/Doom Eternal is due to the game using mandatory ray tracing for lighting.
It’s possible that we’ll see some patches or mods that improve performance, but at launch it will not be a good deck experience.
To be clear, the steam deck supports some ray tracing and it’s enough to run the game, but the performance impact is too much to run at 30fps.
The more powerful ROG Ally also isn’t able to hold a consistent 30fps either (despite using a way higher tdp on it’s chip), so this isn’t a Deck exclusive issue.