Signal is entirely independent and hasn't been acquired by Amazon or any other big tech company. It remains the gold standard for security/privacy technology (whether it's packaged acceptably for everyone on HN is a different question, and I'm not saying you have to use it).

Matrix protocol, or Element app for iOS

Signal sold out? How so?

Metadata stuff? They still require phone numbers(unlike wickr)

Signal is moving away from phone numbers, developing the components needed to securely provide service via user IDs.

My understanding is that their intended audience is the general public, not crypto-security geeks, and as part of that they wanted integration with existing address books. With a small team, developing all the security and usability was more important than eliminating the phone number piece.

They apparently don't retain any data but the phone number, and I think the registration date and last logon date.