The question is who censorsed the information and was legal. Why do you think the question is why?

We know who. The social media companies did. The question is whether they were doing so at the behest of the government.

Because of a law congress made? If not then how is it a violation of the 1st amendment?

Laws are not the only way that government can violate your rights.

If a random cop stops by your house and tells you to take down the sign on your lawn, the government has violated your rights.

The allegations in the article are of that sort, that government agents were giving direction to private companies on what speech they ought to permit on their platforms.

The first amendment only says congress shall make no law.

The entire second half of the OP explains in detail why there may be a First Amendment case here, including some interesting precedents.

and the second says well regulated militia. The courts care about what their interpretation of the intent of the clause is, not the actual words in the clause.