LO 7.2.6.2 (x64)
Calc, Draw, Writer:
The list of font sizes shows
…9, 10, 10.5, 11, 12…
How to get rid of the entry 10.5 ?
More generally:
How to modify the entries in the list of font sizes?
IMHO, the list cannot be changed easily, unless you want to programming yourself.
However, your question suggests that you often do your formatting as direct formatting.
Avoid direct formatting and start doing your formatting with styles.
Professional text composition with Writer
You are welcome to describe your requirements from practice, so possibly better answers can be given.