Under the assumption your gauge is accurate

Cooling system is full , no air pockets



First you have to see if you adequate coolant flow thru the radiator at operating temperature

Leave the radiator cap loose , not pressurized , while bringing the car up to operating temperature at idle in park

Remove the cap

Above 180 you should see a nice steady flow of coolant across the top of the radiator

If you don’t - Thermostat not opening , water pump issue , collapsed radiator hose


Second , if you have adequate flow like described above

Radiator , as in it’s plugged or not enough capacity to cool properly