Having just upgraded from Kubuntu to Neon, appear to me the desktop it's just the same as before, even if in an intermediate step of the process I have seen a graphically different desktop, icons, effects (i.e. the login screen does have a different look and feel with the transparency, different icons etc).

Need I to check something was not installed, or to add some repository?

Did you carry over your previous /home directory? If so, it will use the configs from your previous setup which includes the look-and-feel themes and settings. In that case, a quick-and-easy way to get back to the defaults would be to use System Settings -> Workspace Theme -> Look And Feel and select either Breeze or Breeze Dark and it will switch the remaining aspects to match.

If you've just been using the default settings, then you shouldn't notice much difference since both Kubuntu and KDE Neon use very similar and very vanilla KDE look-and-feel settings.

Were there specific changes you were expecting to see but didn't? If so, could you share more details (including screenshots where applicable)

This is my current screen with Breeze Dark theme, as was in Kubuntu

https://i.imgur.com/yhocadK.jpg

(btw no way to automatically resize the image? keep sayng can't be more than 720p)
Unfortunately a different "Neon" looke and feel was only in a previous state when the system was yest not up to date since I have had problems with the remaining Kubuntu settings, so I can't have a screenshot right now. What I remember was with bigger and a bit different icons, more transparencies, something like that.

Of course I maintained my home with all settings applications etc, that was the goal in not using a fresh installation but an upgrade from Kubuntu, so to maintain all of this.

Not a big fuss to be clear, my switch to Neon was for the features not l&f, but just asking if I'm missing something.