I'm not sure what else you expect.
This is exactly how it works with #ProtonMail and #Tutanota , too. Probably how it works with all encrypted email services that aren't just flat-out GPG.
If I send you an encrypted email under those services, and you aren't a registered user, all you get is an email link to a Proton or Tuta webmail service that lets you decrypt and reply to the email securely.
Edit to add: If you get such an encrypted email link from a Gmail user, the best solution is to send them a separate email from your encrypted service — Proton or Tuta or whoever — and let them reply to you in your service's encrypted webmail service. That way, you avoid Google.