I do, use Signal if you care about privacy. They are the only game in town when it comes to reasonably secure chat software. Sure, I would prefer a federated alternative but I haven’t found one yet that is always end-to-end encrypted, open source, implements forward secrecy, and is user friendly enough to be used by my grandmother.

Don’t use Matrix the devs knew about sidechannel vulnerabilities and ignored them for years. This is peak negligence and should immediately disqualify you from touching anything security related.