Twitter will remove accounts made to "promote other social platforms" and content that has links or usernames to Facebook, Mastodon, and others (@twittersupport)

@twittersupport:

Twitter will remove accounts made to “promote other social platforms” and content that has links or usernames to Facebook, Mastodon, and others  —  We recognize that many of our users are active on other social media platforms. However, we will no longer allow free promotion of certain social media platforms on Twitter.