Since it's the home Olympics I think there is a chance to have 50-60 million. It won't be Superbowl numbers, but it could very well be around a Presidential debate level.
Here's a thought, will the opening ceremony have self imposed breaks for advertisements, or will the American TV audience just miss parts of their own ceremony.
The US only had about 28 million for Paris 2024. It would take quite the advertising campaign to almost quadruple their viewership, even with a better timeslot.