Recent update to kernel 5.4.0-94 gave black screen for login

[GreyGeek]

I think that you are at a stage we all go through where we know just enough Linux to be dangerous!
It's the old paradigm: How do I get a job? Experience. How do I get experience? Get a job.
Keep plugging along. You'll make it!

[phonic-otg]

Emphasis added.

It would seem to me that the 'pretty sddm login' you installed is the cause of the problem.

I wonder what about it caused the issues? It has been functioning well for quite a while and was removed before this post. Yet, removing it did not fix the issue.
The errors mention Back Lighting and video failure when booting into recovery GUI, yet most things in recovery runs as it should and seems all good, except for the brightness and contrast function keys.
The main issue being, not getting a GUI login for any regular kernel and there are intermittent fixes (posted) that work for one (or a few) login attempts but then reverts to the same issue (trying to recreate the fixes results in failure). The journalctl -p err -b -1 and demsg error lists in post 11 are the source of the issue. Yet every time I search for an answer, they are very old and don't work. For example, in one "solved" post was altering grub with

"quiet acpi_backlight=vendor"

which made things worse, where not even the recovery kernel would boot until I restored the grub file.
My UEFI Live USB with persistence always boots well. I had tried to see if I could fix the issue with boot-repair, which said I need to have the Laptop BIOS in EFI as it was in Legacy. I did that and booted the live with persistence USB that has boot-repair on it. Boot-repair reinstalled grub and made my Micro-SD card install EFI and even put grub on the windows partition. But, the issue remains.
Searching with the Duck and Google always gives the same pages, I have three pages to go to and see if they have a solution. This seems to be an old issue for laptops from way back to 2007.

[phonic-otg]

I just tried a compare of the grub files from the persistent live USB with the full distro USB (phonic-otg) and altered the phonic-otg-USB grub file to look like the other. Only difference was I got boot info with all [OK] until it hung. So no fix. I have noticed that live with persistence USB has bright/dark (F11 & F12) functionality whereas phonic-otg-USB does not, and the "connect to an external monitor (F10)" keeps popping up.

Any way, I have to go on a trip for three days and can't continue on with this until I return. Hopefully someone will have a suggestion or two when I get back.

[phonic-otg]

Further info. I am using my phone to post as I left the laptop home to stop me from being tempted to tinker while away.
Anyway I am in a Farcebook Kubuntu group and there was a post questioning why four updates in two weeks. Some one answered that two of the kernels were addressing issues with the AMD APU where the kernel had booked the boot process. As my Lenovo Flex 6 has an AMD APU, I suspect this is my issue.

[jglen490]

Yep! I'd rather see four updates in two weeks, than none at all. It just means that the devs are paying attention.