I saw the previous questions on Possible missing firmware but in my case, I got few more than previously reported. See picture below. I installed this kernel:
5.4.0-48-generic #52~18.04.1-Ubuntu SMP Thu Sep 10 12:50:22 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
I upgraded the kernel with the hope to solve a flickering screen problem during boot time but also the problem of a black screen (failure to boot). I tried all the listed solutions on these two problems and they did not work for me. So I upgraded the kernel and now it boots on the first try (not the 2nd or 3rd) but the flickering is still there and it takes a lot less time to boot. It doesn't really bother me. I am hoping that the problem will be resolved one day after an update.
I searched for the missing files in the firmware site from a linked question but couldn't find the versions of the missing files referenced in the picture below.
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/amdgpu
I don't have a problem with identifying this post as a duplicate and closing it.
During that install, I got the error in the picture.
linux-firmware
and add these files.