The Citizens United decision doesn't allow corporations to donate unlimited or anonymized funds to campaigns. Citizens United wanted to release and promote an independent, short, anti-Hillary Clinton documentary film, and the decision was that this was protected free speech.
> Citizens United wanted to release and promote an independent, short, anti-Hillary Clinton documentary film, and the decision was that this was protected free speech.
This is what Citizens United wanted, but it's not the outcome of the Supreme Court case.
The outcome of the case was the gutting of BCRA 2002[1], which previously prevented unlimited corporate and union spending in political campaigns. The rest (anonymized funding, "super" PACs) are logical consequences of the overturning of that law and American corporate structure.
So they form a corporation and donate to several Super PACs that are technically (though not functionally) independent from the campaigns they wish to support, and that will do with the money what the campaign would have done (buy millions of dollars' worth of ads on TV and social media).
Technically you are right, they can't donate directly to campaigns by forming a corporation here, but they can get close enough that if you squint you can't tell the difference.
Citizens United wanted to pay for commercials for their movie on cable within 30 days of the last primary election. They were free to distribute their movie as far and as wide as they desired.