I’d Begin To Wonder If The Cooling System Was Properly Refilled And Purged Of Air.
Air in the system can cause overheating and air in thermostat housing (air rises in liquid and the housing is usually at the top) can cause problems with the temperature sensor usually located there.
If the fan is truley not functioning it’s possible it relates to the radiator replacement. The fan(s) were probably unplugged during the repair.
Why was the radiator replaced ?
Was it visibly leaking coolant ?
I know it’s summer, but does the heater work in the car when the gauge is reading both normal temperature and when reading too high ?
What type of shop did the work ?
I wouldn’t keep operating this vehicle until the problem is located and resolved. A minor problem can become a major problem with cooling system defects.