I just installed the update on my 12 Pro Max. It was acting weird so I rebooted after the installation. Ended up have to reboot twice. After the second reboot I go a "Temperature" warning about 3 minutes after I logged in. I turned it off completely, and then took it out of its case. Seemed to cool down in about 5 minutes. Turned the phone back on and it IMMEDIATELY started heating up again.
I originally thought the issue was due to me having the phone on a Qi charger during the update process, but now I'm not so sure.