Could be a head gasket, but also could be something else. Coolant leaking into the combustion chambers can (if sufficiently severe) present as exhaust at the radiator and/or as white smoke at the tailpipe (I believe there is an electronic sniffer for this), and as fouled spark plugs. One can perform a cooling system pressurization test and a combustion chamber leak down test to detect leaks to the combustion chamber. Coolant leaking to the oil should show up in the oil (it froths up like a milkshake, and if really bad “oil” level can rise).
A blocked radiator can cause overheating and newly replaced parts (thermostat, fan switch, etc.) can go bad. An improperly oriented thermostat will give problems. Low coolant will cause overheating. Sometimes water pumps stop working (plastic impellers, if it has one, can spin on the shaft). Is the serpentine belt intact, not slipping?
Either you or a competent mechanic should check these before concluding it’s a head gasket, which are pricey. If it is a head gasket, it’s recommended to replace both of them.