While jiggering about trying to get some things running (Vulkan, amdgpu, Homeworld RM, etc) I performed a system update (pacman -Syu). I got amdgpu loaded and running vulkan according to lspci and vulkaninfo. However, after a reboot, everything except Homeworld Remastered launcher looks like the attached image.
(https://i.postimg.cc/CKL63xNy/Very-Broken-Update.png)
I can see that the display is trying to render something (small screen color changes when typing login password for example). This only occurs on amdgpu driver. Everything works fine when radeon is the selected driver. Installing mesa 23.1.4 from the arch linux archive also seems to allow amdgpu to function properly, albeit vulkan demos still show the same effect (see above image again). Did I break something somewhere or is this a bug? I know amdvlk dropped support for my gpu a while back, maybe something similar happened here?
System spec:
CPU: Intel I7-4810MQ
GPU: Radeon HD 8790M
Artix with kernel 6.4.12-artix1-1 and Runit
Plasma/X11 with Kwin
After playing around a bit, it seems installing and using 6.1.49-lts kernel has solved all problems reported above.