I have been in Estonia for a few months and get my TRP recently. It's new to me. But I heard that it's the same. It's just a notification probably. Yet, the term "forwarding address" makes me think it can be something else. I did not get any email from there yet, so I don't know actually.

The PKI thing includes a physical ID card, a software solution called Smart-ID and a mobile solutions called Mobile ID. The software solutions are just authenticator apps that you've matched with your ID.