Herein lies the problem: Trump does not want to block his critics from expressing their thoughts - he can't do that anyway. Nor can he truly block them from seeing his tweets. He wants their replies not to be part of the conversation started by his tweets. They can still comment, on their own pages, in their own articles, but their comments will not have similar visibility to the people that follow Donald Trump and related conversations.
And I think the court overreached to call it a violation of the rights to free speech. Because what the commenters really want is visibility, they want to piggy back on the large audience Trump's tweets have and exploit the way Twitter's algorithm highlights such replies, especially if they are 'considered important' though their own retweets, likes etc.
For example, I want to produce an one hour rant about how Donald Trump is a cretin that damages the US and the world, and have it uploaded on the White House website - an official communication tool of the US government - so that it has proper visibility. But the White House can rightfully deny that request without violating my freedom of speech. Twitter is a multi-user version of a similar software, which unlike whitehouse.gov is configured by default to allow such posts on other's users pages.