It won't be 4k/120 as the PS5 hardware isn't up to it. (I own one so just being realistic.)
Note you don't need explicit game support to used VRR on PS5. I never really noticed frame-rate issues in 120 Hz mode on my PS5 but enabling VRR (when using a suitable TV) should help smooth any minor issues out.
I just checked out the old Digital Foundry performance review below to remind myself of what they found in terms of frame-rates. When racing they essentially found it perfect and so there wouldn't be anything for VRR to do but it did remind me of the replay issues where it could help. I virtually never watch replays and so forgot about this.
Possibly what you were looking for was the addition of an uncapped frame rate for the quality mode, to see if it could run higher and smooth enough with VRR helping out? That would need in-game support.
