Once upon a time, I did "apt upgrade python-pip3" or something like this (was it just "python-pip"? Or maybe it was "apt upgrade"? It was a couple years ago). Anyway, what I do remember is that it quite literally killed apt: invoking it with any command would lead to a dump of a stack trace with ImportError coming from pip. Apparently, apt uses system-wide pip internally so if you touch it, everything breaks? Don't know, don't much care: since it was just a VM so I simply rolled to the previous snapshot and forgot about the details.

Edit: Ah, apparently the steps to reproduce are: do "apt install python-pip3"; do "apt install python3.8"; when pip3 complains that it's outdated, update it with the command it itself suggests.