@shaun thanks, I found this post earlier and did exactly that – reassigned data to another user in the old cluster.
I’m not using the same PG user across multiple applications, I was performing migration from the stolon based stack to postgres-flex. I wanted to keep my old cluster as it was so I could quickly return to it in case the migration was not successful. In any case I don’t really see why detach insists to delete the user and doesn’t make it optional, eg delete user? [y/n]
Oh, I assume I can also attach more than one cluster by having custom --variable-name? I somehow missed that