Assuming that you’re using a Kaveri-based APU, this is what you need to run to switch from radeon driver to amdgpu:
sudo grubby --args=radeon.cik_support=0 --args=amdgpu.cik_support=1 --update-kernel=ALL
Then reboot.
What this does is update your bootloader (GRUB) to pass radeon.cik_support=0 and amdgpu.cik_support=1 to the Kernel, which tells radeon driver to not initialize and let amdgpu take over for your hardware.
I don’t know why the default is not to use amdgpu for these old hardware, but there might be issues when you switch over. If you want to undo the changes, run:
sudo grubby --remove-args=radeon.cik_support=0 --remove-args=amdgpu.cik_support=1 --update-kernel=ALL
If you could not boot (i.e. black screen), you can edit the kernel command line at GRUB screen by pressing e and manually remove the two added parameters, then press Ctrl-X to boot. Afterwards run the above command to clear them out permanently.
With that said, if this issue was caused by an upgrade (and ideally you verified it), please file a bug so the problem can be fixed by Fedora maintainers.