Apologies, my familiarity with some of the terms of Mastodon are still a bit rough around the edges. By relationships, do you mean your followers and who you follow?
If so, it does seem like your followers is preserved (so long as nothing inhibits the move signal), as for who you follow its not clear on the docs whether that is preserved or not (and I've not done an account move of my own) - but you can export a list of who you're following from your account preferences, and then reimport it on your new account for sure.
Account moves are supposed to trigger an unfollow of your old account and following of your new account so long as whichever software your followers are using supports it (I'm assuming Mastodon does since it's in their docs, not sure about Misskey, Calckey, etc).
Account redirection which is a like an HTTP 302 redirect (as opposed to 301) however, does not do this, or copy who you're following AFAIK.
Are relationships transparently preserved ?
Apologies, my familiarity with some of the terms of Mastodon are still a bit rough around the edges. By relationships, do you mean your followers and who you follow?
If so, it does seem like your followers is preserved (so long as nothing inhibits the move signal), as for who you follow its not clear on the docs whether that is preserved or not (and I've not done an account move of my own) - but you can export a list of who you're following from your account preferences, and then reimport it on your new account for sure.
I don't know exactly the mechanic of current migration, I just know it's not good enough.