All of it needs to go away. It doesn’t work. And it will just scorch behind your cooking area, and turn brown.

At a minimum, they need to remove ALL of the pieces added to the posts between the kitchen & dining room...all sides/verticals.

I would also have put a quartz sill on the window stool (not the ”continuation” piece that they did above the backsplash), and wrapped the quartz around (and surrounding) the window as well.

And @User is absolutely correct. Heed his advice! You need to protect the quartz behind your cooktop. The range/cooktop might have come with a guard that can be mounted for this purpose, or your contractor can mount an after market one. Very important!

Should not have gone behind the cooking appliance and IMO they used too thick a materila for backspalsh . As for the posts those need to have the material removed and I like what Mary is suggesting.

Thank you everyone for the input! And Mary, thanks for the extra effort of the helpful visuaI. Does anyone know if heat from the over the range MW is an issue?

The “heat” from an OTR microwave is a non-issue for a backsplash. Unless it has some type of malfunction and is improperly installed, etc.

Thank you, Mary!

'To my surprise they put it on the posts of the pass-through to dining room - AND on the inside of pass throygh"

What surprises me is why folks are continually surprised at INSTALL. .

There should be NO surprises. These are details considered/NOTED and shown to homeowner to be signed at the time of the template. Well before fabrication and install.

I had my kitchen renovated several years ago and had Silestone quartz counters installed, including a backsplash of the Silestone behind my Samsung gas range that extends to the hood. The rest of my counters have a 4” backsplash of the Silestone. The Silestone backspash never gets warm when I use any burners or use the oven. It looks as good as the day of installation. My kitchen designer and carpenter have designed and installed many similar quartz backsplashes behind the range without issues.
Please let us know how things are remedied with your kitchen.

"And it will just scorch behind your cooking area, and turn brown."

We've got to be wary of catagorical statements such as this. "It depends." is better.

Has engineered stone scorched from an improper installation? Yes, of course. Does natural stone scorch in some installations? Yes. Stainless steel won't burn, but will show heat marks.

It depends on the appliance manufacturer's installation instructions and whether or not they are followed. Not just clearances either. Appliance manufacturers forbid using a pot larger than the outline on the top or as specified. A too-large pot will transfer heat and mark nearly any adjacent surface. Now we've went from designer error to customer abuse.

This nuance is why some never experience scorching and why some do on day one.