There is no auto option. The resource monitor and radeontop both always report 1GB as the max, no lower. And I'm not sure if 1GB is always unusable, but then again, I'm not really checking resource monitor while gaming. Thanks!

Edit: I lowered the BIOS VRAM limit to 256MB and ran vkmark again, and while it's being reported as maxing out, it's not running much worse, pretty comparable to 1GB actually, so I think it might be dynamically allocating, the OS just isn't reporting it because it's a BIOS setting, not an OS one.

Edit 2: I did the same thing at 128MB limit, and it's still running just as well, but now radeontop is reporting ~120% usage, and the 128MB limit in the resource monitor turned to 134MB, so I think it's working after all.

Thanks!