Galleries currently only support interstitial ads with Themes Ads Block.
Some clients are forking the Ads Block (For example IT) and then can choose between no interstitial ads OR having 2 ads blocks.
No ads is usually not an option, and having 2 ads-blocks results in multiple issues:
PB Editor showing both and Editors could pick the wrong one, resulting in ads-issues
Duplicate ads code in the Bundle
potentially different Ads versions (double payload) being loaded
Thank you for the idea, Tina. I understand the need to run custom ads within the gallery and the current forking implications. I will add this to our backlog.