Kubuntu 20.04 - Backscreen on boot after dist-upgrade

I did update my PC with apt update + apt dist-upgrade. After the update a started a VMWare machine and it warned that no hardware graphics was available.

I ran glxinfo and it just showed some errors that it could not find a device, and then a decided to give a reboot a try.

• Rebooted, asked for boot password, accepted and got stuck on a black screen.
• Rebooted another time and ended again with a black screen
• Rebooted - grub menu and selected the normal option
  • 
• Rebooted again -> grub menu and selected an ealier entrypoint from timeshift
  • 1 december 2021 13:22:39 (vmlinuz-5.11.0-40-generic & initrd.img-5.11.0-40-generic)
  • With this version I can fully boot into Kubuntu
  • (I think it's version 5.11.0-41 that is causing the problems)
• Tried to edit /etc/default/grub to GRUB_CMDLINE_LINUX_DEFAULT="quiet nomodeset" + sudo update-grub
  • This did not change anything and ended up with black screen again
• Tried sudo update-initramfs -u
  • This ended with errors:

Can someone help me about what's wrong and how I can repair this? For now I'm running with one from timeshift. PC was intalled for about a year ago and I have updated a lot of times since.

System: OS = Kubuntu 20.04

• Everything is encrypted incl boot
• brtfs file system
• timeshift is installed

Graphics = GeForce GTX 1050 Ti (NVIDIA-SMI 470.86)
chp@workstation:~$ prime-select query => nvidia

A post mentioned that the update-initramfs could fail if there was not enough space on /boot.
At a run with apt autoremove timeshift screwed badly up in things and i could not boot at all anymore.
Booted to a live disk and from there with chroot it was possible to cleanup /boot and generate new update-initramfs.
Timeshift made a lot of problems where the OS looked to drop or lock the file systems, so I ended up with purgeing 'timeshift' and 'timeshift-autosnap-apt'.