Adding my 2 cents:
GrapheneOS has 3 update channels, the "stable" channel normally gets an update roughly twice a month. I am on Beta, only Alpha updates every day.
You can set automatic reboots and requirements for updates, so you could totally wait to reboot once the update is installed, and then the process starts if you dont need your phon.
"Require the device to be charging" could be useful here.
GrapheneOS ships updates like they are important, unlike nearly all other Android vendors. This is great.
The optimization of apps after the update is (afaik) because Android apps use Java (not sure if exclusively, afaik there are rust apps) which is an interpreted language. That interpretation takes time and resources, so the apps are precompiled for your device which makes stuff smoother.
The playstore does this too when installing apps, but only for code pages that are used very often, afaik.
You dont need to restart the apps once they are precompiled. You can, but you can also totally wait until you want to.
The "getting hot" must be a Google Tensor thing. My 7pro got incredibly hot too, my 6a doesnt. I hope they have fixed their chips when the 6a gets EOL 🥲