Update to KDE Neon 6.2 broke everything

Hi there. I got the notification to upgrade to the Ubuntu 24.04 base for KDE Neon, which I agreed to. It then started the update, and went without problem, but then complained about some incompatibilities with a custom repository (mozilla). Then it stopped working.
I tried restarting it, but it didn’t work.
I removed the mozilla repository, but it didn’t work.
I ran sudo pkcon update, and it finished without any problems.
I then restarted the computer, and it booted into a black screen.
I did a backup of my data and downloaded the newest .iso file to reinstall it from scratch, but it still boots into a black screen. When trying to do a manual partition, it complains about my efi partition only being around 100MB instead of the required 300MB (it came that way with windows 11 installed).
Trying to install another KDE distro (Opensuse Tumbleweed) gives me a secure boot failure.

Anything that I can do to get it working again? I have to start teaching at an agricultural course tomorrow for a week, and i have to startup windows to do it (at leat that still works).

Sidenote: if any KDE Neon developer reads this: it would be a good idea to either disable the screen lock in the live CD, or give people some hint on how to unlock it once it kicks in… That would be VERY nice, as it would reduce the bother by about 5000%…

Sidenote 2: as an added bonus to my already quite interesting life, i cant’ boot into efi, so I can’t disable secure boot nor change any other settings, like adding a secure efi file or such…

you can try editing the boot options to remove the “splash” (see here [fixed] 24.04 LTS upgrade broke my system: black screen, no cursor, ssh available - #2 by madmaxoft)

Thanks a lot, that did the trick!