There is no better way to get engagement than Facebook these days. People don’t sign into forums on websites like they once did,
I don't know, I've never tried to create a public forum for this kind of thing, but I'd bet you'd get more activity out of facebook than some bespoke web forum or IRC/Matrix/what have you.
We live in a disgusting scenario, we're held hostage by a racket.
But I don't see it as viable as a sole outreach platform for that reason.