... because sometimes you can't see the forest for the trees ... :
I just looked at your plan again and a completely new, simple idea came to me. With your window problem (is there perhaps even a radiator underneath?) there’s a very simple solution: just leave out the cross cabinets under the window and extend the two rows into the corner. In terms of storage, it's practically the same and you get rid of all the height problems. You also don't need to make corner panels. At the end of the row, you would probably still fit an 80 cm drawer cabinet ;) and can also extend shelves for your cookbooks into the corner. If it were our kitchen, I’d prefer to do it that way.
You could maybe use the open space in front of the window for a small table with two chairs. In our kitchen, we have a very narrow table attached to the kitchen unit, fixed to the wall, with one support leg in front and space for 2 to 3 chairs. We use it very often, sometimes we have breakfast there, or in the evening there’s a little kitchen party, for example now with tarte flambée and Federweißer, you sit around comfortably and wait for the next tarte flambée to come out of the oven.
We don’t like dark countertops. Google it, the darker the countertop, the more and sooner you see dirt and especially signs of wear like small scratches.
... and you can almost never have enough workspace. It’s not just about working, usually there are loads of appliances on it: stand mixer, microwave, kettle, toaster, coffee machine – everyone has different things that have to be ready to use at all times.