Wouldn't you match the other far end of the backsplash where it is level with the bottom of the cabinets and goes past them? But NOT to the corner...only to the end of the countertop.

So the 2nd photo.

Thank you! That was my first thought

Agreed. You get points for being consistent.

I would not do a backsplash there you do not need one where there is no water issues . The design is IMO all wrong and why did the cabinets stop there and why no drawers for the base ones IMO bascksplash is eaxactly that no need if no splashing is happening I would not call attention that area

regardless of where you decide to end the tile I would paint the cabinet wall on both ends, a deep blue to match the new tile color. all the way to the ceiling and down to the base, to camo the gapping mistake of the cabinet placement.

It is a shame that you didn't think this through before you installed such beautiful materials.