This fellow might be a contender:
The pilots who fly trans-Pacific cargo are often a couple thousand miles from land accompanied by just one other person who’s within arm’s length. So yin & yang. Doubtless there’s some ship (or sub) closer to them both than the nearest land, and perhaps as close as directly below them, so 6-ish miles away. And the occasional other airplane out there.
I’ve not done that, but I have taken an empty airplane across the middle of the Gulf of Mexico up to 300 miles from land. Enough other airplanes around there I was probably within 50, and maybe even 30 miles of somebody the whole time.
After we set aside the very few Apollo command module pilots who did solo lunar orbits while their pals were exploring the surface, the wackos who do solo transoceanic sailing are probably the true thread winners. But even then there are planes overhead and ships elsewhere on that ocean. Even if the sailor has no idea where they are.