[Vuejs]-Backend with self-signed certificate

Do I inevitably have to have a backend accessible from outside with a proper let’s encrypt certificate ?

Yes, that is the case. This does not necessarily mean you have to change your backend service, you can do SSL termination for your backend through traefik. Setting up Let’s Encrypt through traefik is fully automated process, it should be fairly easy.

Think about it – HTTPS is not just a “nice to have” feature, it is essential for security. All communication over public networks should only be done securely.