Indeed. And, for what it’s worth, we have a request to add that to the FW BIOS on the forums here: BIOS Feature Request: Add ability to specify UMA size on AMD APUs
By the way, llama.cpp now supports dynamic VRAM allocation on the APUs: ROCm AMD Unified Memory Architecture (UMA) handling by ekg · Pull Request #4449 · ggerganov/llama.cpp · GitHub
Unfortunately, it doesn’t look like there are any StableDiffusion implementations that do that as well.