First, the other comments about graphics cards are probably right. But second, if that is a multi-core CPU (not GPU in this case), your system won't tell you how heavily loaded each individual CPU is at the moment. Instead the task monitor normally gives you the aggregate. If you have 4 cores (4 threads) then one thread fully saturated would show as about 25% CPU load. For 4 cores, 20% saturation usually means 1 core at 80% and all other cores idle.
Before I retired, I ran an 8-core IA64 server for the U.S. Navy. I could never get it loaded above about 1.5 cores saturated out of 8 available. That task manager just doesn't normally show individual threads. And in fact if you focused on one, it wouldn't tell you much anyway, because "round-robin" CPU schedule would mean you would only use that CPU for every eighth task-scheduler event.