I was able to get a 580 working with the patched 6.13 kernel and by using ubuntu 24.04 repos for desktop environment/mesa. See AMD Radeon RX550 GPU not working - #23 by skmp for details.
Also note that a friend replicated this setup with a 550 and it needs the esos.elf from 2.1.1 not 2.2 for some reason.
Not sure if a W6400 would work though, there may be more things at play there.