I'd been thinking Telegram would be a sufficiently secure alternative, but as Western intelligence gets their hooks into that system I think we need to go self-hosted. Element is the biggest name here, but I'm curious what options are the best for a combination of both security and feature maturity.
Matrix also also really, really bad when it comes to metadata. I would not trust Matrix when it comes to sensitive things or communication that can be used against you due to how much metadata it leaks. I also find the double standard here were people don't trust Signal due to funding but ignore funding issues in Matrix.