I agree we have an activist court in the Roberts court. How is this making an ex-post facto law, though? The suit is over a bill passed with broad bipartisan support by Congress.
Prosaically, what individual or group is being declared guilty here? The law requires TikTok to have new ownership; it doesn’t seize it, or set a price for it, which might therefore harm shareholders. Calling this attainder seems like a pretty big stretch to me. And, it seems Bytedance legal counsel didn’t think this would fly as well.
The difference here is that Tik Tok is not being accused of a crime and is not being punished for some crime. It's applying a restriction on foreign ownership not to punish Tik Tok for some past act, but because Congress is worried about the risks arising from that ownership in the future.
> However, the Court has emphasized that legislation does not violate the Bill of Attainder Clause simply because it places legal burdens on a specific individual or group.2 Rather, as discussed in more detail below, a bill of attainder must also inflict punishment.
Divestment isn't a punishment for a crime. Nobody is accusing Tik Tok of having committed a crime. Congress simply doesn't want a foreign power hostile to the U.S. to control a business that's popular in the U.S.
People who for decades subscribed to the notion that "emanations from penumbras" are a source of constitutional law don't have any room to talk about judicial activism.
It started with the Marshall Court and never stopped.