My Pi 4 has got stuck during an upgrade. I just did 'apt update' followed by 'apt upgrade' (after 'sudo -i') and it went entirely normally until:-
Adding 'diversion of /boot/fixup4x.dat to /usr/share/rpikernelhack/fixup4x.dat by rpikernelhack' Adding 'diversion of /boot/LICENCE.broadcom to /usr/share/rpikernelhack/LICENCE.broadcom by rpikernelhack' Unpacking raspberrypi-bootloader (1.20201201-1) over (1.20201022-1) ... Setting up raspberrypi-kernel (1.20201201-1) ... Removing 'diversion of /boot/kernel.img to /usr/share/rpikernelhack/kernel.img by rpikernelhack'
... and that's it, stuck at 52% progress.
The Pi is still running, I can ssh into it from another terminal window and things seem fairly normal but I'm not sure how to progress/finish the upgrade.
This is an early Pi 4 with only 1Gb memory.