Well that’s not a problem with Passkeys, that’s a problem with implementation. The ones I use are saved to a password manager and can be used anywhere that password manager is installed.

Yeah it should be “Password+TOTP”

If I’m honest, it’s not convenient either. I stopped using it years ago because I kept getting logged out of my accounts and flagged for “automated activity”. Plus they straight up lie about supporting SMS and RCS. The only “support” they have is connecting it to your Google account.

Theoretically no, all of your messages stored on Beeper servers are encrypted. But they will get all your metadata.

But I wouldn’t worry about that anyway since Discord not only has access to all of your messages but sells them to companies to process for AI. So that’d be the far easier and faster route for them.

Not only is it possible, but people are already doing it.

Depends if you consider Signal “popular”, because based on your own link, the only information they provide is:

No message content., Date and time a user registered. Last date of a user’s connectivity to the service.

There’s privacy and then there’s user experience. UX on Matrix is awful. Not to mention Matrix collects all the metadata, and the vast majority of it sits on a single server (matrix.org), which is owned by a private company and subject to subpoenas.