Heating of iPhone 13 pro max after update to 15.6.1

The 15.6.1 update was only security patches. Do you have any VPN or other security apps installed that could now be incompatible?

Some other considerations if it continues to be hot...

User tip  by LD150

The last update killed my battery! - Apple Community

Same problem here! Especially when on LTE cellular data! iPhone 13 Pro Max iOS 15.6.1