Android - Drag to change route in Google Maps
I figured out that the only way to get around not being able to drag and change your route on the Google Maps app for Android, is to add multiple destinations. This is how you do it (according to Google support, with my CORRECTIONS added in)! ;)
Add multiple destinations: Open the Google Maps app maps. Search for your destination or tap it on the map. In the bottom right, tap the blue circle. It'll show a car, bus, bike, taxi, or person walking. Start the navigation. In the bottom right, tap the little icon with the three dots in a column, and "search along route". Then "search for more places." The search bar will appear at the top, and you will have to type in the intersection where you want to stop or "detour" to. You can also add a specific place, like a restaurant, for example. Touch the location on the map when it pops up, and then "add stop" at the bottom right. Now it will alter your route to include that stop along the way! PRESTO! :)
You can (EDIT: are SUPPOSED to be able to) add up to 9 stops (but I haven't figured this out yet because it won't let me add any more than ONE STOP)! Directions to multiple destinations, or waypoints, aren’t available for public transit or rides. To change the order of your stops, find the destination you want to move and then touch and hold Reorder and then drag the destination. You can search for places along your route.
I HOPE THIS HELPS! "HAPPY MAPPING!!" :D
You can't drag in-route points of a given Google Maps for Android route, you can instead drag departure and arrival spots 'A/B' spots. Drag in-route points is indeed a very interesting feature, but not available in Google Maps for Android yet.
You can drag the markers by doing:
(click images for larger variant when needed)
Open Google Maps and tap "Direction" icon:
Select either "My location" or a point in the map:
In the example, I selected a point in the map:
Same step with destination:
You touch wherever you want the point in the map:
Tap the button to get the route:
When you see the departure/arrival green markers in the screen, you can just tap and hold to drag them to other locations. The route will get auto-updated to new locations.