Activitypub makes it next to impossible to “move” an instance to a new domain.

Every post/comment/and user is uniquely identified using the domain. In the eyes of ActivityPub changing the domain just makes each of those things a completely new thing.

You can set up a new service at your new domain and potentially get most all your users to migrate but they’ll be leaving behind their entire histories and as a “new” fediverse user they’ll only be discoverable via the historical posts for as long as the original server is reachable.