"At both the Tweet level and the account level, we will remove any free promotion of prohibited 3rd-party social media platforms, such as linking out (i.e. using URLs) to any of the below platforms on Twitter,
or providing your handle without a URL:"
https://help.twitter.com/en/rules-and-policies/social-platforms-policy
They're not banning accounts that are not solely made to link offsite but you will still be penalized for mentioning/linking an account of these competitors.
"If violations of this policy are an isolated incident or first offense, we may take a number of actions ranging from requiring deletion of one or more Tweets to temporarily locking account(s). Any subsequent offenses will result in permanent suspension."