I have a 3090 TI and I was actually going to ask about the same thing in the comments. For some reason it won't use more than like 13 gigs of vram out of my 24, and if I make the resolution bigger than 512 by 768 or something around that it gives the "ran out of vram error" 
Like it says that it tied to allocate 3.7 more but it also clearly says I have 7.9 available.
But honestly 512 by 768 is good enough for me just playing around I don't really mind that much.