I read this not long ago, maybe a year. It was either a short story or a novella, certainly not longer. Read in English, in the US.
The story was definitely older though, no clue exactly when but probably before the 2000s. (I remember very yellow crackly pages in my copy)
One quote that I distinctly remember was something along the lines of:
They said that Daniel Boone would pick up and move camp if he saw the smoke from another man's fire. Compared to Boone, < main-character-name > was pathologically gregarious.
(I don't remember the main character's name)
The book opened with the main character (an old man) living on a mostly abandoned world. I don't remember the exact setting, but it was barren of sapient life. There were animals that were like a cross between a racoon, komodo dragon, and velociraptor. They were sentient and hostile to humans, but the main character had somehow tamed them so they didn't attack him.
A woman visits the man, asking for his help with something. I'm fairly certain it's not explicitly stated in the story yet, but the man understands what she wants. He refuses.
It turns out there are two rival factions warring for control of pretty much everything, and he doesn't want to participate in the war. Furthermore, he doesn't trust the woman to be who she claims to be (she says she's from faction A, but she might be from B)
At some point in here another man appears, heavily injured and unconscious. I don't remember much about this, except I'm fairly certain the woman kills the unconscious man.
The story culminates with the reveal of the a piece of technology. This is some sort of wristband that allows the wearer to warp between parallel Earths. The old man's version of the device was older and in the form of a belt.
There was an asteroid. In different versions of the Earths, the asteroid went from overshooting it on the right, to hitting the edge, to full-on collision, then hitting the left edge, to missing, etc.
The old man was living on a planet where the asteroid had come close enough to obliterate life, but not actually hit and destroy the planet.
The woman turned out to be evil (shocker amirite) and stole something (I think) from the old man. He chased her, and she kept running and warping from world to world. At some point they even warped to a place where the asteroid had completely destroyed the planet and there wasn't even an atmosphere.
At the end, it turns out the old man was the creator of this technology. He couldn't live in a world with that tech being constantly used, so he left to live like a hermit on an Earth far away. He had created the device, and another person had refined it into a lightweight wrist device.
He spared the woman and told her to leave, but she still tried to kill him. She failed, and I'm fairly certain the old man just left her for the komodo-racoon-raptor beasts to kill. He packed up camp and left for a more distant world, possibly using up the rest of his device's battery.
At the end, the leader of the pack of the komodoraptors was implied to have gained human-like intelligence, implying that it would start a dog-eat-dog style civilization.
Lastly, I'm fairly certain the reason the old man didn't like the technology was because he thought it would lead (spoiler: it did) to humanity exterminating other versions of humanity and pretty much any other animals they came across, cutting off their future and preventing them from evolving further. The ending possibly implied that he realized what the komodo lizards would become, but maybe not.
I'm fairly certain I read this story in a collection of short stories from assorted authors, again in the US about 6 months to a year ago.