Squeaking sound Toyota Camry, not the belts.?

It could be pulley bearing if the car is at idle.

I believe you already replace the belt and adjust it as it should be. Please use a long screwdriver, attach it to moving part of the engine, and listen carefully to fin out where the squeaking come from. I think it's come from too tight belt or power steering pump. On power steering pump, more warm engine more fluids being circulating, by less fluid cause nothing do lubricating the pump.

if you took it to a mechanic and the mechanics don't know what it is, it's going to be something less obvious.

It's doubtful that people on the internet who can't even look or hear your car is going to guess it.

Go to another mechanic (hopefully a toyota specialist) who maybe able to diagnose it.