Prius T4 UK Coolant Overflow from the expansion Tank

I have a Prius T4 UK model.
3 months ago i got a warning for EGR system. I cleaned the manifold, throtle body, egr valve, pipe and egr coolar. so, no more issues.
About 2 months ago i got RED overheat warning symbol appear on dashboard for couple of seconds on the motoway, i reduce my speed to 65 miles and it disappear. it happened 2/3 times at the same place on motoway going uphill. i checked the water pump and the rotar was stuck, BUT I DIDNOT RECEIVED ANY ERROR CODE. so, i changed the water pump.
My car have done 216k plus miles.
Now, my coolant is getting low and overflow from expansion tank. i keep on checking and toping it up. some time the coolant on the oustside of reservoir is bubbling.
i manualy checked the cap but didnot find any issue.when i shake cap it produce clicking noise.
i put a OBDII device and keep checking the coolant temperature which generally remain between 85 to 90 degree Celsius. when on motoway it goes up to 94 max but comes down afterwards.
So, i need guidance what should i do, change thermostat or cap or ....
All suggestions and advises appreciated.
Thanks

 

it’s original used Toyota I think they replaced the rotor