I couldn't tell who was more uncomfortable, Colbert or Scarlett Johansson. Worse, the interview lasted for two segments. Elon Musk, on the other hand, got only one segment, but Colbert obviously had a lot to ask him and looked like he was having fun. (It was Musk who looked and sounded trapped.)
Without his old character, Colbert has no default point of view from which to pose questions (or make outrageous statements that trigger a discussion). He'd better find the hook that will let him pull off celebrity puff interviews, or people like me will turn away from the unwatchable mess he makes of them.
The other option, of course, would be for him to have complete control of booking, but CBS isn't going to let him indulge himself the way Comedy Central let Jon Stewart. (Stewart, incidentally, often coasted through interviews with Hollywood types who were on promotional tours, but he explicitly made a joke out of his tepid interest in such interviews. Colbert doesn't have that out.)