I'm looking for time travel or alternate universe/world travel where there are two of the main character. So something like where a future/older version meets and helps his/her younger/past self. Or something like where the MC meets and helps his/her alternate reality counterpart. I'm fine with web novel, originals, fanfic, etc. (NU, RR, SV, SB, FF, AO3, SO, WN, etc.) Like these: Remnant's Reclaimer Relic of the Future I'm Still Here
I am not sure if the interaction should be ongoing, or something that happens from time to time ... Sadly I have no idea about the name but someone mentioned some time ago a novel where a person is 'split' into three and each lives in another world and they can communicate with themselves ... survival world, 'normal' world and magic world - me thinks ... However, you could always read Michael Moorcock's books/series as the main plot is (are) the Eternal Champion and sometimes their reincarnations interact - not really the same person, but ... still the same Champion ... somehow ...
Hmm, maybe Life Mission ? This is not exactly it but close: Haunted Duke’s Daughter - The transmigator ends up in a game/novel world, but not as a being but as a ghost haunting the vileness. And she helps to put the vileness in order and fix her mistakes.
If you're okay with webcomics and a homosexual based story (it's not smut, and it isn't a over-the-top "us versus them" romance. It has actual plot, developments that, while they influence the story at large, aren't a direct result of the MC or their actions, outsiders reacting to the relationship for their own, perfectly understandable, reasons and side characters who receive just as much attention and detail as the main pair), then I have an actually good story for you. It's called Leif & Thorn. Time Traveler with two of himself running around is Thorn. He seems to have permission to do so (it's got some details to it), but it's also stated that people who change time often cause unintended side effects. Also there's a "minor" side character who both manages Time Travel. To Quote the manager of Time Travel: "I thought we established that future-me is a dick." "What about past-you?" "Past-me doesn't appreciate that I'm annoying her for the sake of the greater good."