Hetzner would be equally bad idea because sensitive data should be selfhosted and inaccessible to any corporation

This would ban most of computing tbh

By cross platform i mean that you can send message from one server (e.g. proton mail) to another (e.g. gmail)

This is not possible with signal, or any other messengers because email is a protocol and not a software

Don’t kill emails. They’re the only way of cross-platform communication that we have remaining