@FediTips Thanks, I think I found that further down your move tips page, but I was a bit surprised by this stumbling block !
While I could do A->[C]->B I suspect it will be easier just to find an instance C that I like and do A->C ... and there are some accounts on mastodon.social that I follow and wouldn't be able to see on B ...

@FediTips Though you can't easily move to another instance if that instance has 'suspend' on mastodon.social ... and not all instances seem to publish their suspend/silence lists ...