I cannot find a small notehead in Cubase 14´s score editor.
In Cubase 13 I could do this:
In Cubase 14 all I can find is a “compact notehead”, which is just a tiny bit smaller than the standard one:
If you cannot see the difference, welcome… 
(the last two notes are the ones with the compact head)
You can see the difference between our default and compact noteheads for notes positioned between stave lines when zoomed in. The compact sits exactly on the center of the lines, whereas the default notehead covers the thickness of the stave lines, which is generally a more pleasant look.
If you want smaller noteheads for semantic reasons, you’ll have to convert the notes to gracenotes. There is further control over sizing in Dorico, which we don’t currently provide in Cubase.
What’s your specific use case of requiring smaller noteheads?
I frequently used the small noteheads for snare ghostnotes. My drummer and me prefer that over the usual note in brackets.
Cue notes is another example:
Grace notes unfortunately are no substitute. They are per default notes with no specified length and behave like that. The size on the other hand would be perfect!
The ghost notes case would indeed require a custom notehead size mechanism, which is a potential future feature.
For proper cues, Dorico does provide a much deeper automatic feature, which is unlikely to ever make it into Cubase, as it doesn’t fit well conceptually. A custom notehead size would certainly then allow you to give the appearance of a cue, but I worry slightly whether you are trying to use the wrong tool for the job at that point.
so what would be the right tool?
Dorico offers a powerful tool to create dynamic cues, which don’t duplicate the musical data and draw correctly.
Short term, Cubase 13.? Would save you some large outlay, but probably not a longer term solution. There again, I don’t know how well Dorico Elements might fit the bill for this particular use case @StefanFuhrmann ..?
On another note - wonder if SB could consider setting up a ‘rent-to-own’ purchase option (like NotePerformer) or a 3 to 4 instalments ‘payment plan’ scheme to gain access to Dorico Pro more readily for some folk…
Just some ideas.