If someone flies the “software engineer” banner seriously, I expect them to have some theoretic knowledge besides the practical one. They would know different programming paradigms (procedural, OOP, FP), know about programming patterns, layers, UML, and at least a programming language or 4 (3 superficial, 1 in-depth).

A software developer can be any random code-monkey picked up from the street that is self-taught and/or had a boot camp of sorts. Nothing wrong with being self-taught or boot camps, as SDs need to eat, but it lacks a certain level or rigor I would expect from a SE.

If both had a certain amount of experience the SD would mostly catch up to the SE, in practice. Not sure if on theoretic knowledge too, but that depends.