I would check the output of dmesg when you get fedora up. and output of lsmod. you can post them here.
lsmod will show us if amdgpu is loaded (I suspect not) and dmesg will show us if firmware files are missing/not at the expected location.
you may be just a modprobe amdgpu && systemctl restart gdm away from it working?
the amd packages on ubuntu don’t really do much except provide some libraries to smooth things over. I’m guessing/hoping you don’t need those. It’ll be apparent with e.g. steam if somethings broken but all you need for graphics to work right is amdgpu and the firmware. The rest of that mess is what you need for games/vulkan/etc.
just fyi. oh, this may also be useful: How To Use RDNA2 on Fedora 33 - #9 by huge_gamer