I've tested on my system and it works. https://wiki.ubuntu.com/Kernel/LTSEnablementStack#Desktop
1. sudo apt install --install-recommends linux-generic
Installs GA kernel 5.4.*
2. Reboot, interrupt grub, in advanced options elect to boot 5.4 based kernel, complete boot. Check that everything works as expected.
If everything is good, you may remove the other kernel flavours.
3. sudo apt remove --purge linux-generic-hwe-20.04 linux-oem-20.04 linux-hwe-* linux-oem-* linux-modules-5.1* linux-modules-5.8.0-* linux-modules-5.6.0-*
Removes HWE kernels
4. Reboot
5. Download amdgpu drivers (20.45 RD - 12/17/2020), extract archive, go to amdgpu-pro-20.45-1188099-ubuntu-20.04 folder
6. sudo ./amdgpu-pro-install -y --opencl=rocr
7. reboot after installation