When I install a Canvas app on my phone, the marker image doesn't appear, unlike in Companion

If you use the InfoWindow you can only get the text with the frame.

You cannot reduce the size and center the InfoWindow under the vehicle because the InfoWindow always displays above the Marker, in your case, the the icon you created with ImageAsset. There isn’t any way to modify this default display using the native tools.

See what you can do with a Marker > Maps

This extension might allow you to provide text where you want it