In the (default) 30fps resolution mode, resolution scales dynamically from 972p (45 percent of 4K) at worst to 1242p at best (looking directly up at the sky, 57.5 percent of 4K). Cutscenes offer more resolution, at up to 1440p.
As you might expect, the 60fps performance mode uses a lower range of internal resolutions, with menus suggesting a 1440p target (in comparison to a 4K target for resolution mode), but actual pixel counts revealing numbers between 648p and 864p upscaled with FSR 2 to 1440p. It's rare to see sub-720p internal resolutions on PS5 as we do here, but cutscenes do at least switch to a 30fps cap and therefore run at higher resolutions.