That's odd, I did subscribe from my instance but I could not see new posts on the subscribed community and I posted message that did not appear here as well.
I'm on an older version (11.3), maybe that's it? I'll try to upgrade but I'm using a packaged version for yunohost and they did not packaged the last version yet.
Since I host a lot of services I tend to avoid manual installs, I would not have time to manage everything...
I chose matrix over signal because of the centralization problem. That being said, I could convert some friends and family to use matrix but a lot of people went to (or already were on it) signal.
After a few months I decided to install a signal bridge on my matrix server so I guess I'm having kind of best of both worlds, even though it's not a perfect solution, it is one acomodating both sides.
EDIT: it really bothered me to use my personal phone number as well so I use an other number I had laying around