I've tried approximating "Virtual Super Resolution" with xrandr and use 200% scaling to get rid of the slowdown, which would have worked if GNOME didn't keep tight grips on screen resolution/framebuffer size -- my manual changes reverted as soon as I got to the display preference panel.
I tried every Ubuntu release for a few years and we're not there yet. 21.04-beta now almost works except that fractional scaling makes it unusably slow.
I hear there is progress on the proprietary NVIDIA driver side. Maybe 21.10 will be the one...