Oof... it actually happened to me and it's not 1 problem but 2 namely :

• you ran out of disk space while updating
• AND one of the messed up packages is one that is required for the upgrade process, e.g. curl or wget (sorry can't recall which it actually is)

so that leaves you in a terrible stable. You can still clean up this mess BUT that's tricky. Basically you have to

• actually find out what's taking up space (often old kernels) or "just" give up on data temporarily (basically you move your /home, or part of it, to a USB stick) via rescue mode (you need to be familiar with the CLI) or remount the disk on another working system
• get the actually missing packages via another working system then install locally (typically dpkg on .deb files but NOT apt get because that requires connectivity and thus packages you do not have anymore) the bare minimum you need then finish the update.

For me it was on a small temporary system (e.g. RPi for HomeAssistant) so it was basically easier to recover from a recent backup after formatting.

It's annoying but it's actually not that bad.

Edit: clarified on the broken state and dpkg vs apt get