KDE Neon stuck at OS Selection

Something like sudo apt update && apt list --upgradable is no problem in KDE neon, because this only syncs the index with the information from the servers.
But then you should either use sudo pkcon update or sudo apt full-upgrade (and not just sudo apt upgrade) in a terminal emulator like Konsole for KDE neon to install updated packages.
You can see the man pages for further information.