I guess I'll just chime in and regurgitate.
Started having this issue a while ago, shortly after DR16 left the Beta - now, it seems like a dice roll, sometimes Davinci just jumps up about 1 or 2 GB in VRAM usage (for reasons unclear to me) and locks me out of working due to having reached "the maximum". You got more than 5 GB of VRAM left, Resolve, don't be so anxious. It seems to often pop up when I scrub through not fully cached Fusion clips. Sometimes I can totally work for days without any problems whatsoever, though.
Other various info - I mostly work on Full HD content. A few or a dozen Fusion nodes, a few more CC nodes typically, you know the deal. Hope this gets fixed eventually. Otherwise such a great software
Windows 10 - Treadripper 1920X - 32 GB RAM - 3x RTX 2070 (8 GB)
...and no, I won't switch away from Nvidia. I need 'em lol