I feel like the answer is not that hard... someone just needs to make a copy of the basic functionality of twitter with better intentions and not owned by Musk et al. If they are sufficiently trustworthy and competent in how they do it, I really believe that lots of people would be willing and even eager to jump ship immediately.
Mastodon and others tried to do this but they keep spending all this energy on decentralization which is not the problem to solve. The problem is just to be Twitter but (a) not shit, (b) trustworthy, and (c) prosocial. People want to move, just give them somewhere to go and demonstrate more empathy for them than twitter does (not hard).
Implementing this should not be too hard in the AI era and considering that a lot of people would probably donate engineering effort to a Twitter replacement. Paying for it is of course annoying, especially at scale but maybe that's solvable (ideally with a donation model / raising money from people who want to see it exist instead of taking outside investment, or at least limiting the influence of investors so you don't end up making Twitter again). Running it should be easy, just "try to do a good job" (I volunteer, but I don't even use Twitter so I'd probably not be a good candidate). Getting sued for patent violations or something might be a real problem, but maybe it's circumventable, I dunno.
It often feels like every knew large-scale project is corrupted by the Silicon valley funding model (yes I know I'm on a site that has a lot to d with that), so everyone has lost any trust that a new thing will ever be benevolent... but seriously it is not that hard to start a website, that's what Twitter and Reddit and all them did back in the day. The problem is aligning the site to people's morals enough that everybody hypes you up for free. Which ... I think things have gotten so bad now that one could get a lot of free labor if you even start moving in this direction and seem like a serious contender. Although all the VCs are trying to cash in, all the other 'normal' people really just want to live in a safe and happy world where institutions operate prosocially instead of the opposite, and they'll often do whatever they can to manifest that... if somebody just makes it easy to do.