Outlook 2016 hangs updating inbox
Booting a Mac into safe mode is easy, just hold down the SHIFT key on system boot until you see the bootup progress bar, then let go.Safe Mode will clear out some caches and disable some functionality, but it can often be a helpful troubleshooting measure.
I ran into variants of the download trouble several times.
The forced shut down and forced reboot procedure is a measure of last resort and should not be used as a means of initiating any normal restart or shut down process.
Some users have resolved the hanging on shutdown issue by rebooting into Safe Mode.
You can also try disconnecting all external devices, which has been reported to help some users shut down Mac OS Sierra.
The other option is to forcibly shut down and reboot the Mac by holding down the Power key.
This can happen right after the initial installation, but also during a standard Mac system restart after having updated to Sierra.