Am I understanding this right: this app takes a picture of your ID card or passport and the feeds it to some ML algorithm to figure out whether the document is real plus some additional stuff like address verification?
Depending on where you’re located, you might try and file a GDPR complaint against this. I’m not a lawyer but I work with the DSO for our company and routinely piss off people by raising concerns about whatever stupid tool marketing or BI tried to implement without asking anyone, and I think unless you work somewhere that falls under one of the exceptions for GDPR art. 5 §1 you have a pretty good case there because that request seems definitely excessive and not strictly necessary.
Posteo is from Germany and they’re reasonably popular here. Their offer is quite different from Proton, though. If you want full E2E encryption you need to use GPG or S/MIME and handle that yourself (and obviously so does your recipient), so it’s not as batteries included as what Proton offered.
I like their focus on green energy and sustainability though.
Another option like that is mailbox.org. They’re presenting themselves as a bit more business-like.