Boundaries are in place to protect you. Ultimatum’s are used to either force a person into compliance with you or create some sort of negative consequence.

I realize the intent is different. Maybe not. Boundaries are for self protection, ultimatum’s are also a form of protection. I mean the methodology and execution is wrong. But isn’t the intent the same?

What is different about the execution? Meaning this is a non negotiable issue for the person its compliance or a change in the relationship. either diminished importance or walking away completely.

This could be in an established relationship you were never comfortable in or in new and budding ones.