Earlier quoted context omitted.
Hah, I ran into that same upgrade breakage a few weeks ago too! I'm still cleaning up some of the mess but was mostly back within half a day.
What kind of break is this? Is it like you can't even boot into the tty, can't get from tty to graphical environment or just your user applications stopped working?
However, I'm an old DOS nerd so mashing keys on boot is one of the first things I try. Pop has a bootloader that let me revert to the previous something, I guess that's an older kernel? And that loaded right up and got me into the GUI and all my apps worked and everything. So from there I found the "incomplete upgrade" support page, ran those commands, and rebooted again and tried the newer kernel again, and it came right up, all fixed.