I don't really see the issue, 'bubble', is a buzzword for what we used to call a community. You want to shrink viral online platforms to health, which is to say to a sustainable size of trusted and high quality contributors. Unqualified growth is the logic of both cancer and for-profit social media platforms, not of a functioning community of human beings.
Bluesky and Mastodon are a significantly more pleasant experience than Twitter or the Youtube comment section exactly because they turn most people away. If I were to manage a programming project, give me ten reliably contributors rather than a horde of slop programmers.
It was horrible. Being on Mastodon was one of the most corrosive, humorless, joyless, anxiety and guilt inducing experiences I've ever had.