afaik, none. I have pinged the current & recent Oxford students that I know- so far none know of any American med students, though one recent grad said that there might have been one a few years ago, and there are a few that I haven’t heard back from yet.
You have asked this question many, many times, hijacking at least 3 threads. Is this because you would like to go to Oxford for medicine?
If so, is your thinking that if somebody else did it, so can you? if so, that is a distraction: your chances of getting into Oxford medicine are completely unrelated to how many Americans have gotten in over recent admissions cycles.
Also, on another thread you ask if the prestige of Oxford would exempt it from the rules for foreign trained doctors, and the answer is no, it won’t. The info is here: https://www.aafp.org/medical-school-residency/residency/apply/img.html
If you think that you are a seriously strong candidate, start a thread, put your stats and other info up and ask for people to help consider your likelihood of making it past the first hurdle. Of course that (+ your personal statement & LoR) just qualifies you to keep going forward. The BMAT is critical for getting an interview, and the interview is critical for getting an offer.