I assume you normally start route planning by long-pressing on the map and then selecting "Directions", right?

Try a different approach: open the menu (the three-line icon) and select "Directions" there.

The route planner will open. Although the start point is initially set to "My Location", no route is calculated yet because there is no destination.

Tap "My Location" and you will get the standard selection options. Choose "Chose a point on the map", move the map to your desired starting location, and tap "Select". "My Location" will be replaced with "Position on map". Then enter the destination in the same way.

Alternatively, after opening the route planner, you can tap the trash bin icon. This removes the default "My Location" entry and replaces it with "Enter a starting point". However, that requires one extra tap...