Is there such a thing as a "healthy" internet community? I'd argue not. So much of our society's ills these days is people not dealing face-to-face
The formula for a healthy online community is
(0) you must base the community on something objective, a skill like "we are great at (video game)", not something like an idea or opinion.
(1) An actual, real threat of exclusion that's acted on. You cannot include people who don't express the community goals, such as being helpful to each other and growing skills together. (Some great small communities are based around the game Rust, the last place you'd expect to find them)
(2) Excluded people must lose something. Whether it's losing the ability to play with high quality players, or losing advice on knitting patterns
I would also recommend small communities. You can pretty much never create a large healthy online community. Some outliers like Day[9] exist, but as a rule, they don't.
/s