If TikTok were sold to an American company, as the new law demands, why would that change anything about the amount of pro-Palestinian content? Just because the ADL said they don't like TikTok does not mean that's the motivation for the bill. You're still allowed to criticize Israel as much as you were a decade ago (which is to say, less than you're allowed to criticize the US, for some reason ;) but still).
Which big US social media company operates without some form of involvement with the ADL?
This isn't a conspiracy, the ADL openly admits and is proud of their involvement in censorship.
Here they are bragging about their role in youtube censorship:
https://www.adl.org/resources/press-release/adl-applauds-goo...
Google search results censorship:
https://www.adl.org/resources/news/can-google-search-be-used...
X may be the one exception, though I note that the "advertiser boycott" was ended when Musk made trips to Israel, was photographed next Netanyahu's atrocity propaganda prop pieces, next to Ben Shapiro, etc.
Because a sale is and has always been impossible since it would be an unacceptable embarrassment for China in the current climate. The divestiture is just a way to make the ban pass muster.