> The Bosarges’ $5 million mummy now is **in exhibition** at the Museum of Natural History in Houston. ([source][1])

I am not familiar with "in exhibition". I would always use "on exhibition". My own research on Google Ngrams and Google Books is inconclusive, showing "in exhibition" being far less common. I am not sure "in exhibition" means exactly the same as "on exhibition".

Do people say "in exhibition"?

  [1]: https://www.cnbc.com/2020/05/06/how-marie-and-ed-bosarges-divorce-spotlights-south-dakotas-asset-trusts.html