The 2012 Mac mini didn’t have a discrete GPU iirc, just the built in HD 4000
I just looked it up - your memory is correct. Only the 2011 models had a discrete GPU (and only on certain models).
But the HD 4000 is still a GPU and it will be faster than the CPU at certain tasks such as video processing in Plex (I'm guessing that's what OP cares about?)