How high off the ground is the top of the window? The longest multi-stage ladder, of which I would recommend the Gorilla Ladder version, is about 26’ fully extended which means when folded into the most stable position (in half) the top rung should be about 12’. With all four feet on the ground you should easily be able to stand on the very top and reach between 18’-20’ depending on how tall you are. Unlike conventional A-Frame ladders, the multi-stage ladders are more stable and you can easily work from the top rung without there being a balance issue.
Worst case scenario from there is to use a pole, but with you now being a lot closer to the top, you should not have to extend your pole fully and be dealing with a lot of flex. If you did some straight pulls with a pole from the top of the ladder you should be able to clean the window and get great results. Look into a swivel handle like a wag tail or a Moerman excelerator. I use an 18 inch Excelerator with a Fliq pad and Liquidator channel on my commercial higher flat glass panes. The nice thing about the Fliq pad is, if you screw up, you flop it back over the squeegee rubber and you soap again. You don’t have to collapse your pole to swap the squeegee for the strip washer and vice versa. Practice is the only way to get any better. If you have to wash the same window multiple times, so be it.