If system uses an APU, SC2 detects “UMA Frame buffer” as it is the only VRAM available, so it wrongly prevents you to use high resolution textures, despite the GPU actually allocates as much VRAM it is needed dynamically from main system memory in UMA (unified memory architecture) mode.
The most easy to deploy solution to prevent this limitation, it is to remove the enforced texture resolution based on detected VRAM, adding just a warning rather than enforce setting.