I have Kubuntu 20.4.4. installed with Neon desktop.
Today and yesterday Discover is updating some Gnome packages, although there was never Gnome desktop installed on this system.
Is there any reason /explanation why there are Gnome 40 and 41 updates required for Plasma to run?
Additionally these updates are 250-350MB in size, not only small items...

You must have some Gtk/Gnome software installed via Flatpak or Snap. What you are seeing are dependencies analogous to all the tiny but numerous set of package dependencies needed when installing similar software from standard Deb files.