I use Komoot for my primary planner. It took me a while to learn techniques that work for me.
I almost always use the one-way choice and rarely want to return the same way I traveled out, but there are some routes that are just better or more convenient.
The best tip is to select your start point, then select a point on your route and make that the destination. Check the segment and add waypoints if necessary to modify it to your liking. Then select a new point further along your route and choose 'Set as New Endpoint'. Modify that segment if necessary and repeat until you are back where you started or at your new destination.
I typically zoom in pretty far when setting waypoints to get them as precise as I can.
Most of my plans are local rides, but not always in my area. I sometimes drive somewhere and ride in that area. I sometimes check the Strava heat maps to get an idea of popular routes as a start. I have used Komoot to plan multi-day routes as well, but my circumstances do not give me many consecutive nights away from home right now.
I have only used Komoot's voice navigation a few times, but found it quite helpful when I am in an unfamiliar location. It can be annoying if you are intentionally deviating from the planned route with the intention of rejoining later.
I hope that made sense.
Willie