No to either shiplap or crown. Why do you think "they look disproportionate". They look fine to me as they are in a kitchen above the countertop.

I would extend the backsplash

Upward...

I’d also continue the backsplash to the same height as the other wall’s backsplash, which looks awesome! I’d add crown moulding from top of cabinets to ceiling including above the windows. I’d add down light wall sconces (3?) above the windows. What a great kitchen!

Thank you! I can envision that and think that would make it look more finished.

You are right in noticing something is off. The backsplash is ending in a random spot and the contrasting green wall color throws off the balance... Extending the backsplash upwards is going to help a bit but not solve the lack of balance... My suggestion is to REMOVE the bit of backsplash in red and PAINT the entire wall with windows and door in the same color as the backsplash(white). The windows will then dissapear visually.

Always nice when someone posts the results from their original question. Looks very nice.