Does Go F Yourself mean “I Never Want to do Business With You?”
Are these companies in any way whatsoever required to buy advertising on X?
You miss the point.
Of course they are not required to buy advertising on X. Though by withdrawing advertising they are further injecting themselves into social and political issues. In this particular case it was about Musk commenting on a tweet that wasn’t really anti-Semitic, but his enemies tried to portray it as such. In fact, Chuck Schumer went on the Senate floor and basically said the same thing the tweet said that “Jewish Americans feel left alone by their political allies on the left”.
Musk is mocking them, though, saying “I’m the richest man in the world, you can’t force me to change my stance on free speech by withholding advertising dollars to X” - and at the same time taking the offense by saying to them “let’s see what ‘the people of earth’ will think about your efforts to mischaracterize free speech and let them decide”.