I posted this feature request to enable more VRAM: BIOS Feature Request: Add ability to specify UMA size on AMD APUs .
The BIOS change is particularly necessary for Linux, and applications and libraries not capable (yet?) of dynamically requesting more VRAM from the system. The AMD’s ROCm framework and PyTorch libraries used for machine learning, unfortunately, are prominently in that category at the moment. The situation with games seems to be better, both on Windows and using Vulkan on Linux: many of them are able to get the VRAM allocated as needed.