Overheating?

Hello, it sounds like you have had everything replaced that has to do with the cooling system, you might want to have a back pressure test done at the front Oxygen sensor opening to see if the Catalytic Converter has failed and is partially blocking off the exhaust. A back pressure test at that location should not be more than 1 or 2 psi. Testing at the front oxygen sensor location is before any of the Catalytic Converters so it will show how much pressure is building up.

Thats pretty strange for the coolant temperature sensor housing to melt. I assume it was probably made of plastic. Are you noticing any lack of power now that the problem sounds like it has gotten worse?

You can also try a chemical head gasket test at the radiator, I know you had the head gaskets done, but if there is a crack somewhere even in the engine block that the mechanic didn't notice it will be the same effect as a bad head gasket. The chemical test is cheap, and it will tell you if there are any combustion gases getting into the cooling system. I will post a picture of the chemical test to give you an idea of what it looks like. It's also called a Block Test.
One other thing, what were the codes present?

There was a Recall as well on one of the Air Bags too, just for your information, it is an old one (2014), so it may have been done already.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

https://www.2carpros.com/articles/head-gasket-blown-test

In the morning when the vehicle is cooled off, have you verified it's not low on coolant? There is a bleed screw, although since you've been having issues even before the work was done, I don't think that's the issue.
Do you know if the mechanic had the cylinder heads sent out to be checked for cracks or warpage? Usually when head gaskets are done, the cylinder heads are resurfaced to make sure they are perfectly flat. And then also checked for cracks. It should be on the repair order they gave you from the shop. Does it still overheat at 60mph? Or just at idle now?

And if it's just at idle are the cooling fans coming on? Since the coolant temperature sensor melted, I would check the wiring harness in that area as well. Something is not right if it's still overheating. Either the fans are not coming on while it's sitting idle, or something else is happening. There are only so many things it can be. I'm assuming the Temperature gauge is going hot and/or the light is coming on. Make sure the wiring harness is not melted anywhere, causing the coolant sensor to possibly short out. If you have the means of verifying the actual temperature around where the coolant temperature sensor is, as well as the thermostat area to see if it's actually overheating or if the temperature sensor is giving a false reading. Both fans would be on high if the sensor is giving a false reading because that is the only means for the engine computer to determine coolant temperature. Check it with the A/C off.

Also, if you just had all this work done, technically, the shop that did the work misdiagnosed the issue. And should now find and repair the real issue at their expense. This is not your fault.

That's where I would start, a meltdown, especially if the wiring harness got overheated and the wiring inside some of the conduit is burned will put resistance in the coolant temperature sensor circuit and the sensor itself works on only resistance. It changes resistance as it heats up or cools down. So, any additional resistance in the circuit is going to send a false reading to the engine computer (ECM). And if you want to get really technical, we can do some voltage drop readings from the sensor to the ECM connector with a basic multimeter. Getting a voltage drop reading while the vehicle is running and hot, is the only way to know if the circuit has any issues. Check the coolant sensor harness plug, hopefully it was changed out, if it was hot enough to melt the housing for the sensor, there was definitely damage to the harness. You didn't happen to get any pictures of the damage before the repairs by chance?
I'm very surprised there were no codes in a situation like that.

There is some Self-Test on the Instrument Cluster info, states that the light won't come on until 255 degrees, at that temperature, the air coming out the vents would be extremely hot.