The executive branch's broad authority to regulate foreign commerce has been a constitutional privilege from the beginning - Jefferson strongly advocated for it, for example. Only legislation would disallow this order from going through.

Then the lawsuit will fail, and the system works. What is the problem, then?

Even when the judiciary system works as it's supposed to, that doesn't necessarily mean that justice is being fairly delivered, which would mean there is a problem with the law itself. I think detractors here are misunderstanding what is currently the law and what they think should be the law, in this case.

What laws are those?

Whichever ones TikTok is using to sue? Either they have a case or they don’t, but they still deserve their day in court.