I don't use Facebook, so I can't say about that. I don't really go on-line for political discussion at all.
The idea that we somehow will be able to encounter a diverse range of opinions we disagree with but we are open to from people outside our tribe is asking a whole lot from both you and the outsiders.
Finding other sources of community and content that isn't centered around a feed is a good idea as well.
There are multiple other factors beyond algo or yourself. 1 study I saw proving echo chambers used reddit r/history where their moderators enforce an echo chamber on purpose. They go way beyond banning viewpoints like holocaust denial. Even basic misunderstandings of non-controversial history are banned. Thus resulting in a objective echo chamber.
That same study went to look at more controversial subs and places like r/canada where moderators ban people for viewpoints they too have an objective echo chamber.
From my point of view echo chambers have been objectively proven to exist. In some cases that's the intention but ultimately echo chambers certainly exist.