Fedora 34 won't use Radeon RX 5500

I have a desktop with an AMD Ryzen 7 3700X processor and a Radeon RX 5500 GPU. It worked fine in Fedora 33. I installed Fedora 34 over the NVMe disk (didn’t do an upgrade) and had to use the simple graphics installer so ended up with nomodeset on the kernel command line. Booting that way gives me a screen 1024x768 which is much less than the monitor size. Booting without nomodeset gives a black screen. vdpauinfo says “Failed to open VDPAU backend libvdpau_nvidia.so: … no such file”. Well, no, it’s a Radeon. vainfo fails with “driver_name = (null)”. lspci shows “VGA compatible controller: Advanced Micro… [Radeon RX 5500…” as expected so the GPU is talking to the bus. radeontool regs shows a long list of registers. Xorg.0.log shows errors:
open /dev/dri/card0: no such card or directory (indeed, there is no /dev/dri)
Unable to find a valid framebuffer device
Screen0 deleted because of no matching config section

I added selinux=0 to the kernel command line to eliminate that as a possible cause. So the hardware is clearly there. There is no other GPU and the MB does not have any integrated graphics. I understand that nomodeset will force simple graphics, which is what happens, but I’m in the dark (literally!) with the black screen I get without nomodeset. Any ideas?

Hm, well, I installed Fedora 33 over the NVMe disk and got the same result. I hate to think the GPU has failed, it’s expensive. Anybody know how to tell for sure?

One quick easy way to be to boot a live USB with distro with good current graphics support and see if the device is working. If it is, it should be possible to get it working with Fedora.

The solution had nothing to do with software. In case it might help someone, I’ll describe what happened.

First, I was reluctant to believe that such an expensive part had failed after only six months of use. I took it to PC Laptops here in Salt Lake City and asked if they could test it. They did, on a different computer running Windows, and the Radeon GPU worked perfectly. This helped me a lot, and they didn’t charge for their service, so you can take this as a plug for PC Laptops if you like.

I took the GPU home and reinstalled it. As I did so I noticed that the little tab with the hole that accepts a screw to hold the card to the back of the case did not line up with the screw hole in the case, and if I tried to force the card into alignment, it would lift the inside end of the card slightly in the PCIe socket on the MB. So I didn’t use the screw, and since the socket has a latch to hold the inside end of the card, the screw didn’t really seem necessary. As a result the GPU is now running perfectly on Fedora 34.