FWIW, and I apologize if someone has already brought this up, but to cite Jonathan Kirsch:
“‘Jew’ is a term derived from the tribe of Judah and refers to the descendants of the tribe who survived invasions, conquests, and dispersions that resulted in the destruction of ten of the twelve tribes.”
By this logic, an Israelite who was of a different tribe (such as a Levite) would technically not be a “Jew.”
They are more like ethnicities that aspire to ethno-nationalism.
What’s the difference, you ask? Well, it is this: in most cases, you can’t “convert” to become (say) Basque, if you were not already. Also, if you are Basque, it is not usually possible to cease being Basque simply by an act of will - that is, to walk into a Church Basque, convert to something else, and walk out non-Basque.
A better example would be a purely “tribal” identity, like being Iroquois. Most people are born that way, but at least in the past it was possible (albeit not easy) to be adopted by the tribe, if you meet their criteria and agree to be bound by their rules - whereupon you become “Iroquois” yourself.
Judaism is somewhat like that.
Unlike say Islam, you can’t become Jewish merely by an expression of belief - you have to find some congregation willing to accept you, and it usually isn’t encouraged. However, once accepted, you are just as “Jewish” as those born into it [and those born Jews who treat converts differently, who do exist (there are always some people like that), are in the wrong according to the Rules™].