Thank you @v-bacao-msft for the links.
Yes I mean that this field can only fill the content manually, and can't use Expression to modify the content.
My scenario cannot have users adding expressions in that field. (Users can ignore the hint).
Error codes and error messages hinder user experience, but if my ask is not possible this would seem the way to go.
Can you provide an example of giving error messages using a condition like mine?