Although KDE neon is based on Ubuntu 18.04 (and now 20.04) it doesn’t recommend using the same method to update. In Ubuntu you generally use some form of the application apt. Either in a GUI with the software installer or on a terminal emulator with a command such as,
sudo apt update && sudo apt upgrade
These commands work in Neon but you will find after a while that there will be packages not being updated with lines like, “Dependencies are not satisfied for…” and then the package name. What is happening is one of the differences between Neon and Ubuntu are being exposed. To quote the official recommendation,
KDE neon does continuous deployment of the latest KDE software which means there are nearly always new versions of our software to update to. We recommend using Plasma Discover’s updater which appears in your panel:KDE neon
You might not have noticed this if you were using Discover already. I tend to use the command line though so the held back packages were popping up.
The official guideline on updating KDE neon on the command line is to use the same updater as Discover and issue the commands,
sudo pkcon refresh && sudo pkcon update
This was written for KDE Neon 18.04 but the same applies for 20.04. This advice is in the KDE Neon FAQ as well so if you are thinking of linking to a page it would be best to link to the official page at https://neon.kde.org/faq#command-to-update.