I'm fine with paying for it, but what's worse is that the notifications aren't end-to-end encrypted, and the plaintext passes through their server and Google's.
For some use cases where self hosting is required for compliance reasons, this is a deal breaker. And spinning your own mobile apps isn't quite practical.
We're very actively working on end-to-end encryption for notifications; it'll be in the Zulip 11.0 release this summer if at all possible.
While I'm here, the Flutter rewrite of the mobile app is launching next month, and while the initial launch won't add much functionality over the previous React Native apps, the rewrite is way faster, less buggy, and a lot more pleasant to add new features to.
For some use cases where self hosting is required for compliance reasons, this is a deal breaker. And spinning your own mobile apps isn't quite practical.