I have thought a tooon about this stuff and yeah I think any form of nationalization is not a serious proposal, and 99.9% of the people offering it would back away from it at the trivial thought experiment of a Trump 2024 win - hmm, that guy, in charge of twitter's festering not-quite-dead-yet carcass? Yeah, no.
What I do think would work is a carefully set up internationally accountable nonprofit, in the mold of Wikipedia. Which is not to say that wikipedia doesn't have tons of cultural issues that most of its volunteer editors could tell you all about, but WP is at least as socially important (if not as powerful, in the various ways twitter was acknowledged to be powerful back in its heyday) as twitter and it has managed to keep its head above water in an incredibly turbulent sea of competing geopolitical-cultural forces.
The funny thing is that in a lot of respects (but "total expenses" probably not being one of them), a non-shit version of twitter should have lower overhead than wikipedia. You could basically roll back all the terrible bullshit Musk did to it and be within spitting distance of a feature complete version you could call "beta" and missing some moderation features. Twitter as a piece of software could basically be "finished" and do just about everything its users want it to do if it didn't have to turn a profit - all the "likes are now florps, timeline goes sideways" bullshit was the product of the Dorsey administration's rudderless R&D churn. The ongoing costs of content moderation and hosting would be the main thing a Twitter Foundation would need to put out the hat for during fundraising season. And I think it'd probably do fine for revenue if the entity asking for money was more like WP or NPR than Musk's incredibly inept grift.
Everything that would be fraught and politicized about a nonprofit (no really, actually nonprofit not all this neolib market-focused bullshit) Twitter is already fraught and politicized about Wikipedia (eg what's on Xi Jinping's page and who gets to write it). You would need to build the team very carefully and monitor its ideology, and it would be under constant attack from undemocratic forces of every stripe, but again this is true of multiple currently existing entities.
My best case scenario for twitter's epilogue after Musk finishes defiling it and sells off its corpse would be converting it into this sort of entity. I don't have much confidence that'll happen but it's what should happen, dammit.