That FPS sound very, very low for AC. AC usually runs very well, so something has to be wrong. In fact, even with CSP+SOL I’m managing 60fps at Wide FOV on my 3080ti in the most demanding situations (rain at night.) I don’t know what’s gone wrong though; maybe try a complete default reinstall of AC? (Backup your user and game folders first so you can revert if you wish.) You aren’t running PP by accident for AC are you? AC is one of the very few games that does not need PP.
With those specs AC should look great. With a 4090 & i7 7700K i have SteamVR at default settings apart from maxRecommendedResolution @ 16384 in the file default.vrsettings, PiTool fov @ Large and Quality @ 1.5, no smart smoothing, Nvidia control panel at default settings, Content Manager MSAA x 4 (rest mainly high), CSP 1.78, SOL 2.1.
You say you have poor resolution, do u use more than 1 vr headset? When i use my quest 2 with SteamVR it messes up SteamVR with my 8KX (the res is very low), i need to reinstall SteamVR.