Answer
Making Sticky Notes genuinely read-only through presentation-object or activity permissions isn't achievable — despite the "Read Only Allowed" label, that setting doesn't block editing in practice. A practical lockdown alternative ahead of a migration: add a Custom Event on insert/update of the underlying notes table that raises an explicit error message (via Error_SYS.Record_General) telling users Sticky Notes can no longer be created or updated, which effectively blocks the action even though it isn't a true read-only permission.