Emergency mode error

Volumio does not start after a power failure.
It’s in emergency mode, but I can’t fix it according to the descriptions given there.
The machine is an x86 PC (HP t520), the system is on an SSD.
If I type “systemctl default” it goes back to the beginning “you are in emergency mode”.
The “systemctl reboot” command does not work and the “exit” command does not enter default mode either, emergency mode starts in the same way.
I get a “dpkg error” message after the “dpkg reconfigure” command.

Can anyone help me avoid having to reinstall the system?

I am sorry to tell you this, but trying to recover a crashed system is unpredictable.
You have no insight to which extend things are broken. With a bit of luck you get it booted again but end up in an unstable/failing system.
Please run a clean install