Can you place an Augmented Reality Anchor in a private apple indoor map? https://register.apple.com/resources/indoor/program/indoor_maps https://developer.apple.com/augmented-reality/tools/
Augmented Reality in the indoor map program
If you are referring to Location Anchors, those can be placed outdoors in areas where GeoTracking is supported (see the list of supported regions)..
For AR experiences where you want to anchor virtual content at a known indoor location, I recommend checking out ARWorldMaps and the Saving and Loading World Data sample. This is independent of Indoor Maps. You could however use Indoor Maps to first determine the coarse location (e.g., the room that the user is currently in), and then switch to an ARSession and relocalize to the saved ARWorldMap.