Comment 7 for bug 1760128

If you are hit by this issue, it seems sufficient to simply ask dpkg to finish configuration as it seems the prerm script isn't retried

$ dpkg --configure -a

Or you can just re-run your upgrade command (e.g. "apt upgrade") which should do the same plus finish any upgrades that didn't finish (which may be the case) - you'll probably want to do that either way.