Disable the default font sizes (S, M, L, ….) for blocks

Hi,

I have a custom post type, let’s call it “Book”, and I need at least for paragraph and heading blocks the defailt font size selector (S, M, L…) leaving only the custom selector. This way the font size is added directly into the HTML as a style.

I’ve looked at the documentation and tried many combinations (add_theme_support, filter on theme.json, …) without success. Can it be disabled?

I need this only for that CPT without affecting the regular working mode of the theme and blocks.

Thanks, Stefano.