I have been hearing that matrix dendrite is no longer being worked on (at least unless people volunteer). I know that you cannot use element x which isn’t a big loss for me. I only plan to use it for family, friends, possibly friends and family of friends.
The big loss for me would be in the privacy category of things.
I have tried getting synapse to work but only managed to have it work with sqlite3 database. I don’t know how to get it to communicate properly with my postgres database for some reason. (I am using docker on ubuntu).
It won’t get less secure, but you’ll likely miss out on future improvements that would make your instance more secure.