That sounds pretty shakey. Federal employees have their own email addresses, but you can't just go ask for a .gov email address, you have to get a job with the government for one. The federal government has plenty of places that only some are allowed to post to. Now, if they were to say, only allow certain people to have accounts with no apperent rhyme or reason that would be grounds for a discrimination lawsuit, but they could simply say "any verified current or former federal elected official, federal department head, or state governor is allowed an account" and expand or shrink the scope as needed. The fediverse honestly makes that so much cleaner than something they host themselves with all of the nuances of what is and isn't federated, the government could simply configure the federation to meet their legal and liability needs while users can stream in from any fediverse instance

are you allowed to post on whitehouse.gov?