It's a lot more than what's listed in the title. Basically every major social media platform is in scope here.

The FBI?

That is still too kind. The insurrection was planned by the same types of corpo-fascist lobbyists that orchestrated the push of "woke", DEI, advocating for illegal immigration, etc. Take legitimately understandable frustrations, radicalize both sides with a culture war of feel-good half solutions that revolve around blaming their neighbors, smash the divided people into one another, and no matter which "side" "wins" the unaccountable corporate power structure ends up advancing.

Online message boards were merely places for recruiting foot soldiers and getting them riled up.