SUMMARY
After the latest upgrade the whole system became unusable except for switching to the console.

STEPS TO REPRODUCE
1. Hard to say, large update in past two weeks with about 1,2 GB of data messed up the whole system
2. pkcon update clearly failing, removing some absolute necessary dependencies
3. apt full-upgrade installing everything, but still not working
4. had to reinstall everything by forcing apt to --reinstall
5. probably some config files from ~/.config were an issue for neon/plasma to fail, I can provide these as I have backed them up
6. once the whole config dir was removed (and everything force reinstalled) the system was usuable again - ofc had to reconfigure everything for hours from the defaults

OBSERVED RESULT
System unusable, both SDDM and plasma unable to boot

EXPECTED RESULT
Everything working

SOFTWARE/OS VERSIONS (after fixing the system)
Operating System: KDE neon 6.0
KDE Plasma Version: 6.0.3
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Kernel Version: 6.5.0-26-generic (64-bit)
Graphics Platform: X11

ADDITIONAL INFORMATION
Various info from the logs or while trying to launch plasmashell (taken from my browser search history) (also a short rant - inability to find clear logs in /var/logs of plasma /kde /neon is tragic for cases like this):
failed to find a kirigami platform plugin for style fusion
binding loop detected
graphsplasmoid does not match the format 
applications.menu not found in Qlist /etc/xdg
offer service offset line 333 kbuildservicefactory (i.e. kbuildsyscoca6 failing with some ASSERT error on this line)
kbuildsycoca6 Q_ASSERT(offer.service()->offset() != 0);
sysdeps unix sysv poll no such file
locale changed to kr_KO.UTF-8 LANG when trying to fix the system (very weird as it wasn't even configured to this before ever) - e.g. after forcing apt to reinstall both neon-desktop and kde-full, plasma-desktop etc.