Proton Docs currently limits the minimum font size to 8 px (drop-down).

Please allow users to enter smaller custom font sizes, such as 7 px or 6 px, instead of enforcing 8 px as the minimum.

Smaller text can be useful in tables with many columns, compact technical documents, reference sheets and other layouts where information density is important.

I understand that very small text may not be suitable for normal body text, but this should be a formatting choice left to the user rather than a hard limitation imposed by the editor.