1.Under settings go to Device Manager>Display Adapters> right click and disable AMD
Radeon (TM) Graphics

2.Start doom eterna

3.The frame rate will be crappy.. stop the game now that it has started (the game can now
“see” the underlying GPU)

4.Now enable the AMD Radeon Graphics (like how you disabled it in the first place)

5.Start doom eternal again..

The game should run smoothly now (at least it did me).

Hope this helps!

https://www.reddit.com/r/Doom/comments/fltsm5/doom_eternal_gpu_driver_error_no_physical_devices/

This doesn't work quite right for me and I have to keep the Radeon Graphics driver off while playing.