Why would anybody use Matrix after reading https://www.hackea.org/notas/matrix.html ?
[1]: https://github.com/libremonde-org/paper-research-privacy-mat...
Needless to say Matrix servers and clients don't send any data (private or otherwise) by default to central servers. The only central services we have are the identity lookup service (i.e. map phone number & email to a matrix ID), which is strictly opt-in and various anonymous stats reporting (which is also strictly opt-in).
Other articles mentions sending metadata only to servers you have users from (which of course can be a problem, but at least is explainable).