@floo214 is right, if you’re using ACF Photo Gallery Field (Which is a separate and unaffiliated plugin from ACF) you’re out luck… an alternative solution would be to use PODS, but instead of creating a separate Content Type, use the “Extend an Existing Content Type” option. Downside to this option is that there are no display rules, like for instance when a post has a category “e.g Movies”, all posts (extended Content Type) will have this field displayed on the backend.