2011 Outback with overheating problem

[HotOutback]

2011 Subaru Outback premium 3.5 4 cyl with CVT transmission. Bought used late (October) 2024 with overheating problem. Car stays in Georgia. No temp guage on dash, just red light which activates at 240 degrees (115 C). Attached an OBD2 scanner to the port under the dash to continuously monitor temp. Shortly after cold start, upper radiator hose very hot, lower hose cold. Replaced thermastat. Same hot/cold hose result. Heater in cabin blowing very hot air at this point. Cut the spring and wax cylinder out of thermastat and reinstalled bare housing. No overheating but also no hot air in cabin, even when OBD2 shows 190 to 200 degree engine temp. Tested coolant for exhaust gases over 3 hour time period with continuous negative results. Drove car 1600 miles October through June without issue. Now in the heat of the summer car is running hotter although within 190 to 220 degree normal operating temp. A few times it was 230 degrees in traffic with the A/C on. Also, coolant from the radiator is filling the overflow up to the top. Coolant in overflow tank transferred back to radiator only to refill over a few days. In the morning when the engine is cold, removing the radiator cap releases a small amount of air under pressure from the radiator. I have suspected head gaskets but can't get a positive exhaust gas reading for the radiator. No coolant in the oil or oil or exhaust gasses in the coolant. Help!