OK, TIL (Today I Learned):
If "apt install" tells you "after this installation, XX GB additional disk space will be used" – that means that YOU SHOULD LOOK if that's available. Because, APT DOES NOT – it simply … well, stops working when the disk is full 🤦♂️
Have fun then cleaning up. Glad I ran a Timeshift backup immediately before…
(EDIT: it was `apt` in my case, not `apt-get`. But such a thing simply should not happen at all.)
