It's public knowledge https://help.twitter.com/en/managing-your-account/help-with-...

> Once you’ve changed your username, it returns to general circulation and may be selected by another account.

So in the case of services where your username is the only thing your account is identified on, it probably makes more sense to delete your tweets and leave the account active. Oh, and post a nonsense message every few months so you don't get deactivated