No, this is the most serious lacking feature IMO.

But you could of course simply register your username at multiple instances and subscribe to the same communities. As there’s no ‘followers’ like on Mastodon, the effect is the same.

If that’s so, these instances (and who knows which other ones in the world) now host OPs and comments that I as an author decided to delete.

How does one delete information from the fediverse? If this is true, you cannot. Your data will be hosted forever, at least somewhere.

If people use their personal name for an account, this might result in a significant GDPR problem for all instances.