Comment 13 for bug 1788727

Forewarning, I began switching to Antergos one day after your post and finished today, so I will not be able to provide any more hands-on data, since Antergos is an Arch-based distribution (tried to install Arch in a VM twice, failed both times). I switched because I was trying to make my Ubuntu install into a rolling one, so why not switch to a proper rolling one, like say Arch (or an Arch-based one, like Antergos). I had to disable Secure Boot though, so it defeats the purpose of this bug (yes, it seems that Arch kernels are unsigned), but whatever.

It seems that you misunderstood me, at least a bit. The older kernels are the ones you're not supposed to remove during this procedure. I am not sure about the upgrade being interrupted by the newer kernels, but I didn't try UKUU before 18.04 anyway (speaking of which, did you mean 18.04 when you wrote 20.18?).
Also, the kernels aren't "efi" and "non-efi", they're signed and unsigned, reflecting whether or not they would pass under Secure Boot, though it seems that my laptop doesn't care after GRUB is loaded, which is signed by Canonical as well (speaking of which, what's the model of your laptop? the number should be on the underside of it if it's a newer model, probably 2014 and later, but definitely 2016 and later, mine's 15-aw003nm).

Could you please clarify what your course of action was after installing Ubuntu Artful?

My understanding is that you didn't even touch UKUU (Ubuntu Kernel Update Utility) on Artful before upgrading to Bionic and not even after the upgrade. If that is the case, could you provide a few more details regarding that (the exact or near exact error message, whether or not you have Secure Boot enabled, generally what was going on, ...).
Also, what sort of crash was it? Was it a full system crash or did it affect just a part of the system (also, whether you're using the Ubuntu or Ubuntu on Wayland session, you can check by clicking the cog left of Sign in, since I tend to get an error every time I log into the Xorg session/the default one/the one that is not Wayland on Ubuntu, though not on Antergos oddly enough, and you say it actually prompted for information, which does not happen if it crashes to the extend that some of my experiments made it crash, but only for application crashes and crashes of a similar scale)?

One last thing I just realized. You're replying in an email? How?

Anyway, good luck and have a nice day!