pop os uses the 5.11 kernel, fedora 34 kernel 5.12.
Try a manual update.
i did it for my dell to 5.14 and updated manually all missing firmware i915.
firmware package https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/
One thing I noticed while going through this old system was that it only had 2GB of RAM. I happened to have some memory laying around that worked for this system and after upgrading it to only 4GB of RAM and booting it up the 550RX fired right up.
It appears that this GPU needs more than 2GB of system memory to function.