In the link that
@jcanoe provided, it talks a bit about that.
The NM cables can be used at 90C for temperature corrections, but the circuit can only be rated using the 60C column per NEC 334.80. Another thing to consider is most of the wiring in the attic is attached the ceiling joists and underneath the insulation. You would have to consider that the temperature at that location is likely cooler, maybe around 95F to 105F if the space below is conditioned. Assuming standard 15A circuits using #14 NM, the 90C rating of copper is 25A. The temperature correction of 100F is 0.91 for 90C. 0.91 x 25A = 22.75A. No need to change the wire size. Using this data, the maximum temperature that a #14 NM copper wire could be used in to maintain 15A at 60C is 141-149F. Most ventilated attics won't reach that temperature even if the cables were exposed (not under insulation). Obviously each specific circuit should be analyzed in the same way, especially for larger circuits or continuous load circuits.
I won't go into using a #6 NM for the EV charging circuit in the US as it isn't allowed based on 2017 NEC Section 625 - Electric Vehicle Charging System requiring the circuit and overcurrent protection be sized for continuous duty and have a rating of not less than 125% of the maximum load of the equipment.
*Edit for your use case: #4 NM copper has an ampacity of 95A at 90C. To maintain the 60A at 60C rating, you could install your cable in up to 141-149F temperatures and meet the code (141-149F is a 0.65 derating at 90C - 0.65 x 95A = 61.75A).
For reference, I am a licensed professional engineer in multiple states.
