Mastodon hints: moving to new account Mehr anzeigen
Moving between #mastodon accounts is a bit like moving physically from one place to another.
What you did at your old home (your toots) stays there, plus a note saying "I now live over there".
You take your address book (the list of people you follow) with you, but you need to notify your mutuals to update theirs. Preferably in advance.
If your old home explodes (instance goes down)... then you need a backup of your address book. So: export it regularly.