I just finished a five week bike tour. At times I used the routing my GPS (Garmin 64, Cycle Tour option, minimize ascent option) provided, but for planning I also used the Android App Komoot.

The Komoot app (I used free version) could give me elevation plots, etc. That came in handy in my route planning as I could assess not just distance, but also elevation, where the big hills were, etc. This app for planning had to be on-line.
https://play.google.com/store/apps/d...droid&hl=en_US

But almost every day, I deviated from a recommended route when the GPS or Komoot wanted to take my on some weird loop to avoid what turned out to be a perfectly good road.

Having the Maps.Me app on your Android phone with the maps loaded for the area can also come in handy, that you can use off-line. I do not find their bike routing to be very good, but when my GPS or Komoot were having difficulty finding what looked like a good route, I often checked Maps.Me (free version) as another option.

I have also used the web version of Komoot on my computer with large screen at home, that helped me fine tune routing, etc.
https://www.komoot.com/plan

I am a little perturbed with the Maps.Me app. Several years ago I paid for lifetime ad-fee usage, but they changed their policy to subscription, and they no longer provide me with the lifetime of ad-free usage that I paid for. But that is off topic.

Bottom line, I find that there is no perfect routing method. Sometimes having a paper map in hand can be a good aid.