Hello :-)
I'm doing the same activate and then adding DRI_PRIME=1 in front of wine game's command line, but it isn't working as before. Running Anarchy, latest linux kernel 5.6.3, bios 314 (may need update; am going to check now). Had installed the latest kernel as I'd read that the main GPU's bottle-necking would be fixed in this kernel, but I can't even get the main (RX560) GPU to activate.
Have been reading round, and found that xf86-video-amdgpu needed installing, as did amd-ucode. Reboots have made no difference.
xrandr --listproviders shows 2 providers, but systemctl --state=active | grep radeon shows no text output.
The Vega will run small games really well, but anything larger has a lot of large white patches flickering. Not sure if there are further things that I should install, or if the kernel has a bug/bottle-necking a work in progress still. Would be very grateful for advice.
Thank you
EDIT: have found this thread, which is suggesting xorg isn't loading the GPU ...
https://bbs.archlinux.org/viewtopic.php?id=254475
... and to use a different kernel. Not understanding everything on the thread, and not sure if using pamac to install the linux-amd-staging-drm-next-git kernel, then removing the linux kernel/headers might mess things up. Maybe better to wait for the xorg fix, if that is what is wrong.