Mac mini hangs on Apple logo after Mojave 10.14.6 Update 2

My mac mini (model Late 2012) worked fine until I installed the "Mojave 10.14.6 Update 2" security fix today. After the automatic reboot (required for the update), the boot process hangs after displaying the Apple logo. (There is no progress bar showing up below the logo.)

I already tried resetting the SMC, but that didn't change anything. Booting into "Internet recovery mode" worked and I could run "First aid" over the harddisk, but that didn't fix the problem.

When I boot in verbose mode (Cmd-V), I see the message

Attempting system restart...MACH Reboot
Attempting system restart...MACH Reboot
Attempting system restart...MACH Reboot
Attempting system restart...MACH Reboot
Attempting system restart...MACH Reboot
Attempting system restart...MACH Reboot

repeated endlessly, after a few kernel traces WRT corekrypto.kext.

Unfortunately, I don't have a time machine backup of this Mac.

How can I recover my system? Is there a way to boot of an installation medium and recovery the system without having to reinstall everything?

Thanks a lot for your help!

[EDIT:] I managed to take a video of the boot log. The first error reported is a kernel panic with message "FIPS Kernel POST Failed [...] corekrypto_kext.

Why did the security upgrade leave the system in this state and how can I fix this without having to reinstall everything?

[EDIT 2:] I just found this issue on the net: https://eclecticlight.co/2019/10/18/beware-apple-security-certificates-after-24-october-they-may-have-expired/ Could this be the problem I'm facing? How can I fix the certificate?

Newer hardware can boot to internet recovery and attach an external drive to copy files off.

If you can boot to a recovery partition on that HDD - that would be the fastest method. Otherwise, you’d need to boot your Mini in target disk mode or bring an external bootable OS to it to copy files off before erasing it.

The problem was caused by third party kexts. To fix it, I booted the system in safety mode and removed all third party kexts from /Library/Extensions.

After that, the system bootet normally and finished the upgrade process. Now everything is working perfectly.