How to Boot Previous Linux Kernel

I am crosslinking this thread so you can see that this is not a dire experience or anything:

It is not the kernel at fault, nor a system failure of any kind. Just a bleeping computer annoyance.

Mostly, it seems related to Snap packages. They get stuck in the pipe.
You can jiggle the handle using terminal

sudo snap refresh

If it is a flatpak update doing it (They do this, too):

flatpak update

In addition to @wesoliv429's suggestion to run sudo apt update && sudo apt upgrade