Surprised no one has suggested Knowledge Commons https://hcommons.social as an instance that is a haven for scholarly people. Perhaps more in higher education, but K12 educators would be welcome and well taken care of with the good moderation. Formerly Humanities Commons, it has expanded into STEM education and other fields to be more inclusive. Based at Michigan State University, it has government grants and other support to sustain its services.
I also recommend Knowledge Commons for blogging or maintaining a free Website. I was just starting to discuss research repositories and criticizing Academia Edu at https://hcommons.social/@SteveMcCarty/112609326085901837 without having space to suggest open access alternatives like Knowledge Commons. Its repository welcomes teaching materials, syllabi, and all sorts of genres, to which I've been happy to contribute, at https://hcommons.social/@SteveMcCarty