Aren’t black Ethiopian Jews one of the 12 tribes?
All Jews descend from Israel, but not all who descend from Israel are Jews.
There is evidence that some descendants of Dan left Goshen (in Egypt) before the Hebrews were enslaved and went north to Dodecanese islands region around 1500BC.
After the Kingdom of Israel divided into Israel (north) and Judah (south), Israel was overrun by Assyria and taken away into captivity. No appreciable number ever returned. Where in the world they went is a matter of archaeological interest.
When the (mostly) Judean kingdom was taken away to Babylon, where they were first called “Jews.” Not all returned when they were given permission to do so 70 years later. Many came back, including some of the tribe of Benjamin. These were later conquered by Alexander, and then Rome, and the descendants of this remnant are now known as Jews.
Other Jews who did not return from Babylon became assimilated into other cultures, and lost their Jewish identity.
Those of Israel who went into Assyrian captivity have dissolved into the landscape of other cultures, but they were never before, and should not now, be called “Jews” though certainly they are Hebrew descendants of Israel. Their tracks, to the extent they can be discerned, are a matter of archaeological interest.
To confuse the matter still further, Mosaic Law made provision for foreigners who did not descend from Israel to become followers of Hashem and of the Law of Moses. So, by Roman times, there were among the Israeli-descended Jews, some number of adherents to the Mosaic traditions who would have been called “Jews” who did not have bloodlines connected to Israel.
The state of the entire matter is such that it is possible that people in diverse places around the world could have bloodlines tied to ancient Israel, and they would not have any knowledge of it. Again, that wouldn’t make them Jews, but would link them by blood to Abraham.
Whether these Ethiopians have ties to Israel, himself, by blood or ties by tradition, as foreign adherents to Moses... I don’t even know if DNA could give us a definitive yes or no, but it would be better than relying on tribal hearsay.