gregor on Nostr: Technically, as far as I understand, your account really only consists of your own ...

Technically, as far as I understand, your account really only consists of your own access key, which you can just discard at any time. Regarding the data your created and signed with that key, the individual relays have technical control over if and when they delete it. The protocol supports delete requests, only some clients and relays support it.
While this might sound unfair, it fits the nature of a distributed network like the internet itself. The network remembers forever as long as one participant cares to back up or host the specific information. Words spoken inevitably remain in the mind of anybody who hears them.
If you want to control access to certain information, encrypt it, or keep it off public networks.