Ladder levelers exist. Many of them though appear to only be really effective on steps. I’ve seen it suggested elsewhere that you dig out the high side of the hill there so that the ladder can be leveled that way. So now you get to possibly “call before you dig!”

Another site suggested building or buying scaffolding to put the ladder on. Not sure how effective that’s going to be either. The scaffolding is either going to roll down the hill or sink into the ground. Neither is ideal.

Our house sits on a hill like this so I’ve looked into how to solve this problem before. Settled on a ladder leveler but it still doesn’t seem as sturdy as I’d like. Fortunately there isn’t anything to really do on those sides of the houses. No windows, wires, pipes, etc. The pressure washer reaches to the top just fine.