i'll check when i get back in front of my computer. i want to say 460.7x but that's a guess. its the latest on 20.04 from apt repos.
To your question about updates. so, technically yes i had this behavior when i updated my 18.04 to 20.04 which i didn't suspect would go well...and it didn't go well so i did a fresh build of 20.04 on my asus machine. Then i ran apt update/upgrade and installed pybombs, UHD4.1, gnuradio 3.9 and gr-fosphor master branch. The same issues persisted after that which is why this feels like a driver issue,
i use nvtop to monitor my GPU and it's not going crazy or anything.
also just to add, i did try using GLFW and QT gui fosphor blocks, both did had the same result.
Do you have a known working driver version and any other required packages for this to work on ubuntu 20.04? is installing the driver package from nvidia vs apt any better or worse?