The viscous fan clutch should cut out at around 30 kilometer per hour.
After that speed the airflow through the radiator overcomes the clutch flow.

Last time I had your problem it was the water pump.
I put a erzatz non oem Behr pump (PRC knockoff) in the car - didn't get any better. Changed pump again for a Graf and all overheat problems disappeared. Car ran at 87 - 90 constantly even in very high ambient temperatures.
Fleebay knockoff cheap pumps don't cut the mustard - it's just one of those occasions you have to bite the bullet and get the real item

If you have a minute leak anywhere, the pressure cannot be maintained - the symptoms you describe can also become evident.