I’m generally aware of all that, but I don’t see how it answers the question. Why can’t you just stop all app processes, unmount the relevant partitions, clear any memory containing cryptographic keys etc. but not actually reboot?

Rebooting just seems like a very roundabout, slow and inefficient way to get back to that initial state you describe. Is there something e.g. the bootloader does that cannot be replicated on a running phone and is essential for securing it again after the first unlock?

Why is a reboot necessary for that? Is it not possible to enter the same encrypted state the phone is in after a reboot without actually rebooting?