Can't create custom resolutions after going from 6900xt to 5070ti (LG 27GX790A-B)

[99muppets]

Creating resolutions in SRE, which is what I had used previously, simply doesn't show the resolution anywhere, not in the nvidia control panel, or in my windows display settings. Tried rebooting, tried restart64.exe packaged with CRU, still doesn't work. When I try to create a resolution in the nvidia control panel itself, it says;

Test failed.

Custom resolution blah x blah at 480hz (32-bit) is not supported by your display.

Any ideas? Would really love to use custom resolutions again.