This question reminded me of a very vaguely recalled short story, most likely from the early '00s or '90s (and probably in a magazine like F&SF, Asimov's or Analog), of a space ship that can easily travel incredibly far, galaxies clusters away, in some far future when humans commonly can and do pilot craft that travel above c somehow (I don't recall if this involved some sort of hyperspace or what), colonizing the universe with abandon.
Somehow (obviously this seems incredibly improbable, but I don't recall how this was explained -- perhaps ships had some light-speed-breaking way of detecting other ships?) the handful (2? 3?) people in a first ship randomly encounter in mid-intergalactic-space another human traveler traveling alone in his own ship, and they dock the two ships together. I think they have dinner together in honor of the meeting, but something is off about their new acquaintance (some wort of craziness that slowly reveals itself?), and some sort of conflict occurs.
I think someone on the first ship was working on something like simulating a miniature universe in a computer.
The story got... weird, somehow... toward the end. I think just one character somehow got locked into one of the ships with the controls jammed into taking him far beyond the furthest explored reaches of the universe, and he was just left talking to the computer with no other company. Somehow, he found himself disconnected from interaction the rest of the universe in that far void, where there was no possible return to the realm of galaxies, and local reality seemed to be disintegrating somehow, as the ship had lost its causal connection with the rest of the universe.
I think there was some sort of connection implied between the computer simulation notion and the disintegrating isolated reality state the character ended up in. I don't know if that necessarily meant that we are in a simulation; it may just have been some more philosophical connection.
I think they may have mentioned never having come across another sapient race in all of humanity's vast expansion, but I'm not sure.
Sorry if this is rather vague; it's about all I can remember of the story, and I may be pulling in some detail or two from another story.
I'm pretty sure I didn't read it in the last few years, which is why I place it in the '00s or earlier, and the computer simulation aspect is what makes me think it was '90s or later. It's possible that I read it in some collection, rather than the aforementioned magazines.