Have you found a solution to this problem? I observe a similar behavior. However on my device (iPhone 8 with iOS 14.4) the tiles only appear when canReplaceMapContent is set to false. In addition to that on zoom levels around 8 the tiles do not appear or just a couple of them. Furthermore the map has to be touched and moved a little bit to trigger the loading of the tiles. With iOS 13 everything was working fine, with iOS 14 the code is working in the simulator but not on a physical device.

This is still a problem in iOS 15.3.1. I can however confirm, that the workaround mentioned by Nicolas V is working (mapView.mapType = .standard).