> I’m stuck on integration managers. Are they even still a thing?
I almost never see it used in the public federation; it's mostly a corporate feature. Also the default integration manager is proprietary.
> Also after so many years, there’s only like, four bridges?
https://matrix.org/bridges. You can host yourself, otherwise there's Beeper, and certain public hosted bridges also exist; see also https://joinmatrix.org/guide/features/#all-about-bridges.