Airplane mode for offline map use must be used with offline maps like geospatial pdf's and apps that use offline maps. Currently, I make my geospatial pdf with caltopo (desktop browser) and add the map to topomaps (iOS) for use in the field.

The most common app used these days for this is gaia gps for making the map and field use. Farout (formerly known as Guthook) is another commonly used app for buying maps. Caltopo can now do the same. There are other apps that can read geospatial pdf's, like Avenza and others.

You can't test offline maps use with google maps or apple maps, unless you have made the map for offline use.