Star Trek: Lower Decks really steered into the multi-verse theory to close out their show's run. in the second-to-last episode of the season, the series brought in numerous returning stars from past Star Trek shows. Instead of reprising their roles, however, they all played alternate-reality versions of their original character.
For instance, T'Pol was married for a long time to Charles "Trip" Tucker in her timeline, while one version of Harry Kim was a lieutenant. It was all in good fun but the problem with the multi-verse concept is that it's overdone to such a degree the originality of it has lost its luster.
Not only that, but the point of a story is to follow around a set of characters and see what happens to them. If you could just replace the characters if they were to die or become disinteresting, then you lose the stakes of the moment entirely. While a captivating episode, we saw something similiar with the Voyager episode "Deadlock." In that episode, the Voyager spaceship is duplicated and stuck together, thus creating a whole new set of characters.
On one ship, Harry Kim and an infant Naomi Wildman die, and on the other ship, they don't. So when the end of the episode comes, and one ship is about to blow up, they simply send Kim and the infant Wildman over before they do. Thus, continuing the story despite such major deaths. It's a great episode but the stakes are never as high as we're supposed to believe they are because there's a safety net of sorts for the characters.
That's an issue with the multi-verse theory in science fiction. More importantly, the concept of there being an infinite number of universes where there are slight variants of our world is simply that, a theory. So for Star Trek to steer into it and accept it as fact seems off for Star Trek. We don't know that traveling in time causes there to be a split in reality where two new universes form from that point.
So for Star Trek to steer into that idea seems flawed. It's science fiction, sure, but Star Trek adheres to other laws of science, why are they making such broad allowances for one that isn't even provable? Not only that but the allowance for more alternate realities waters down the story and possibilities.
it was a big deal when the Mirror Universe was introduced. It's still the most talked about alternate reality out there. Then we got the Kelvin Timeline and that already started to water down the concept. Now we're throwing out all pretenses, and we're traveling between realities like we're going to the corner to get some milk.
The more universes fans are asked to juggle, the less fun it's going to be to do so. It's what happened with the Arrowverse on the CW, fans kept getting callbacks to other, better universes and it made what we were seeing on a weekly basis seem lackluster and flat. The same thing is about to happen to Marvel, with their MCU. Fans are going to either long for a different universe to take hold or for things to go back to a pre-Endgame format.
Neither of which is possible. Same with Star Trek. The more universes you open up for fans to explore, the more they're going to be drawn to newer possibilities outside of the established universe. They're going to want something that'll never come and that will sour their experiences with the prime timeline.
Instead of exploring narratives that are outside of the Star Trek norm, they should look to make the best out of the prime timeline before they lose their core audience. The fandom will only take so much shlock before they have had enough. Shows like Strange New Worlds and Prodigy have helped, but if you keep showing them other universes, which are better written or more fondly received, you're going to do nothing but remind the fandom that you aren't capable of giving them what they want.
So it's best to not even broach the idea of possibilities at all.