Of course if the app have done anything seriously illegal it would not have been necessary to bring this law to ban it, because existing laws would have sufficed to do it.

Perhaps because US government wanted to do it despite TikTok not breaking any serious provisions of law this law has been made.

It feels like a sleight of hand from government to ban something that has broke no (serious) law (yet).

Did the SCOTUS go into the necessity of having this law to achieve what government wanted, if existing laws would have sufficed, provided that government met the standards of evidence/proof that those laws demanded.

If not, it is as if government wanted a 'short-cut' to a TikTok ban and SCOTUS approved it, rather than asking government to go the long way to it.

I suggest you read the full 27 page ruling and what I quoted again. Supreme Court doesn’t weigh on the wisdom. But found enough evidence that TikTok does not refute that showed that they were engaging in the conduct that Congress alleged and that the law is not unconstitutional.

Trump tried to ban it first by executive power, but the Supreme Court decided he didn’t have the authority to do that. Then congress passed a law, and the Supreme Court is saying that the law is valid and Trump has no grounds to ask for a pause for him to “work a deal.” Congress could just repeal their law, but other than that it stands.