Flarum has been a piece of absolute dog shite since I had the misfortune of installing it when Seth deleted everything. They have over-promised and under-delivered, and there are a lot of better open source alternatives. People criticize it because it's a significant pain point for the community, as the forum here has historically been the centre of the community, and when it lacks basic functionality to enable a forum to be successful, it gets shit thrown at it.
I would never recommend Flarum to people, and would never willingly support it in the future after the pain of doing so here, it's entire architecture is backwards and it's been poorly engineered. It makes running a community with it's software more difficult than it should be, especially for "Modern" forum suites like it claims to be and to compete in.