It would make sense to call yourself an engineer if it’s your job to engineer things, which by definition means to design any kind of complex system for some kind of practical use.

“Engineering” is not itself a discipline (branch of study), but instead a category of disciplines. Civil, mechanical, industrial, chemical, and electrical are the core five disciplines that people typically associate with the term engineering, but you can engineer complex logical systems as well, like software or computer networks, and an infinite number of others.

My point is that trying to gate by protected title “Engineer” on its own is impractical because it’s just a broad concept. It makes more sense for each discipline to create some sort of licensing system and protected title that conforms to that particular discipline.