For me, I have intel integrated + amd discrete. When I tried to set DRI_PRIME to 0 it complained that 0 was invalid, when I set it to 2 it said it had to be less than the number of GPUs detected (2). After digging in I noticed my cards in /dev/dri/by-path were card1 card2 rather than 0 and 1 like everyone online said they should be. Searching for that I found a few threads like this one that mentioned simpledrm was enabled by default in 6.4.8, which apparently broke some kind of enumeration with amd GPUs. I don’t really understand why, but setting that param made my cards number correctly, and prime selection works again.