MyRoute-app limits routes to a maximum of 200 route points in total (this includes both "shaping points" and "via points"). The distance between these points can be very large; for example, you can have a route with only a start and finish point, which could span thousands of kilometers if it is a direct route.
However, for practical purposes, it is recommended to place waypoints more frequently (e.g., every 5-10 km or 3 miles) to ensure the navigation system follows your intended path exactly, especially when transferring the route to external GPS devices like Garmin, which may have their own, more stringent, limitations (e.g., a 29 via point limit).
If you are planning an extremely long trip that might exceed the 200-point limit, you may need to break the journey into multiple, smaller route segments.