The thermostat tries to keep the coolant temperature at some temperature (e.g. 200F). However, as the ambient temperature increases the cooling performance decreases. The car cooling system is designed with some assumptions and the result is always a compromise between costs and performance. When the power output of the engine is high, the thermal output is also high. At high ambient temperatures, the cooling performance might be at its limits. In such a case, the ability to keep the oil temperature in a normal range might be assured only when the power output is sufficiently low. At high speeds (high thermal power output) the thermostat may be fully open and yet the oil temperature might be significantly elevated.Apparently hot weather doesn’t matter since thermostat will keep engine at certain temperature?
At much lower ambient temperatures I have observed that oil temperature increased from quite stable 200F (195F to 205F) to 260F (with peaks up to 275F) just by increasing the speed from 80 mph to 110 mph. I bet the thermostat tried to keep the temperature lower.
In Saudi Arabia ambient conditions, I would aim for a 5w40 or 0w40 or even 5w50 with approvals like Porsche A40 / C40 etc.