I got that far behind once, except to fix it I told apt I was on the latest Ubuntu release and told it to update. It worked surprisingly well, except that after the upgrade, systemd would pause for exactly 60 seconds before sleeping or shutting down. I thought it was because of my shenanigans, but a fresh install had the same problem, so it was something in that release, and not my method of getting there. I never figured out what caused it, and ended up switching to MX Linux and using sys-v, which has been working great since. I deleted everything except the /usr/ folder and installed MX Linux on the same drive, so from a logged-in desktop everything was set up exactly as it had been in Ubuntu.

Anyway, within a distribution a "release" is really just a list of which version of any given package to use, and anything release-specific is expecting those versions. Even the difference between distributions is just package versions, plus which packages available and which are installed by default. Linux is just packages. If you can update all of the packages at once, you can effectively change which release you're on. If it fails half-way through though, you might be in trouble. You could boot off of a live flash drive, and use chroot to fix everything, but at that point you might as well just do a reinstall, from the live drive.