file explorer not responding

Setting Cinebench to Realtime priority is the most useful clue here. A realtime CPU-bound process can starve normal Windows components, including Explorer, input, remote-control software, and even parts of the desktop. That can look like Smart App Control blocked Explorer when the shell was actually waiting for processor time.

Since Explorer recovered, I would not disable Smart App Control. Open Reliability Monitor and check the time of the freeze for an Explorer, Cinebench, display-driver, or Steam event. Then open Windows Security > App & browser control > Protection history and confirm exactly what was blocked. Remove the blocked Cinebench download and obtain a fresh copy only from Maxon's official page if you still need it.

For another benchmark run, leave priority at Normal or, at most, High. If the shell hangs again after a normal-priority run, restart Windows Explorer from Task Manager and check the display driver and Event Viewer. Realtime priority is not appropriate for a benchmark running inside an interactive Windows session.