Rx 6600xt stuck on Motherboard splash screen

(I am Dualbooting) I recently replaced my Radeon R7 260x with an Rx 6600xt and was hoping it would work without further changes because they are both AMD gpus , but after switching the GPU ,the system gets to the point where you can choose your Os but not any further. When choosing linux as the boot option it shows the Motherboard splash screen again and gets stuck there. The GPU seems to be functional though , because when choosing Windows it works just fine.

I updated to Ubuntu 21.04 , but that didnt really help. Any help would be great :D

(I still have the old Gpu)

The issue is missing firmware. The system actually boots fine, it's just that there is no video (see last paragraph). I was able to fix the issue by updating the kernel to the latest stable mainline release, and by installing the missing AMD GPU firmware files.

What you need to do is this:

1. git clone git://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git I assume here that you run this in your user's home dir.
2. cd /lib/firmware
3. sudo mv amdgpu amdgpu.orig
4. sudo cp -r \~/linux-firmware/amdgpu ./ This assumes you cloned the above linux-firmware in your home dir.
5. Install latest kernel from mainline (I used 5.13.12) - if you need a tutorial see this. Make sure initrd gets regenerated as part of the kernel install. If it doesn't, you may need to run sudo update-initramfs -k all -u

That should do it.

How did I figure it out? Installed openssh-server on my box, then let the 5.13.12 kernel boot and sshd into my box. Ran dmesg and saw that amdgpu driver was complaining of a missing firmware file /lib/firmware/amdgpu/dimgrey_cavefish_sos.bin. Check to see if it's in /lib/firmware. Figured that the kernel Pop OS 21.04/Ubuntu 21.04 ship with don't have this firmware, and the mainline kernel installer doesn't bother updating the linux-firmware package, so I had to get it off git...