The system uses unified memory, which means that the ram is dynamically allocated between the CPU and iGPU depending on where it’s needed.
Some programs will see very little VRAM and throw an error about not having enough VRAM (because the program doesn’t understand that more VRAM will be dynamically allocated when it’s needed). The BIOS setting UMA_GAME_OPTIMIZED (which is poorly named BTW) is to dedicate some VRAM so that those programs see a couple GB of VRAM and don’t throw an error.