@ozfrog
Sorry if I am wrong, I am not an aviation specialist.
The Route planner tool is not what you wish?
https://community.windy.com/topic/9013/windy-launches-route-planner?_=1606767020515
This tool is only available on desktop, not in the phone app.

Capture d’écran 2020-11-30 à 21.21.54.png

You may also have look at Flight planner in the plugin list
Capture d’écran 2020-11-30 à 21.31.41.png