KBExit I can confirm that the native clock's alarm works after reboot (I have mine set to 4 hours), and so does Google Clock's alarm, and Clock's alarm.
In general, if an app supports Direct Boot, then it will work after a reboot, before first unlock (BFU).
Johnnyloans rebooting will get rid of any malware
Just to add to this, rebooting works on malware that tries to stay in memory. But a way to get persistence is to have it delivered via some app already installed, so they can keep reinfecting after reboots too. So it does not remove "any" malware, but only the most common malware types. GOS (and for that matter android) is already significantly hardened against remote exploits, so it is not a worry for 99.99% of people.