That has been the narrative so far. That “subject to the jurisdiction thereof” was so that the spawn of foreign diplomats, who enjoy “diplomatic immunity” from USian laws, would not be citizens.
But look at Justice Barrett’s opinion in the Colorado case. She agreed with the rest of the majority that Colorado did not have authority to prohibit someone being on the ballot, but she dissented in the majority’s use of section five to declare the insurrection clause invalid. She said the court did not need to go that far, to decide the case. If there is no act of Congress to enforce the citizenship clause, it is just as invalid as the insurrection clause. Going to SCOTUS, the same SCOTUS that decided the Colorado case, with that “no enforcing legislation per section five” argument, would be a slam dunk. We would then revert to the citizenship law passed by Congress a few months before the text of the 14th was passed.
Be it enacted . . . , That all persons born in the United States and not subject to any foreign power, excluding Indians not taxed, are hereby declared to be citizens of the United States; and such citizens, of every race and color, without regard to any previous condition of slavery or involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall have the same right, in every State and Territory in the United States, to make and enforce contracts, to sue, be parties, and give evidence, to inherit, purchase, lease, sell, hold, and convey real and personal property, and to full and equal benefit of all laws and proceedings for the security of person and property, as is enjoyed by white citizens, and shall be subject to like punishment, pains, and penalties, and to none other, any law, statute, ordinance, regulation, or custom, to the contrary notwithstanding.
https://constitutioncenter.org/the-constitution/historic-document-library/detail/civil-rights-act-of-1866-april-9-1866-an-act-to-protect-all-persons-in-the-united-states-in-their-civil-rights-and-furnish-the-means-of-their-vindication
That “not subject to any foreign power” would eliminate anyone whose parents were foreigners, thus subject to a “foreign power”.
Steve