The cabinet installers should have made everything level--regardless of the settling of the house. That's what shims (and 1x4s) are for.

The tile installer should have checked this too, in planning the layout.

The small tiles make the problem more obvious by creating a strong grid pattern

Your best option, if it bothers you that much, is to install window trim that overlays the tile. You'll have to plan it so that it stays away from the grout lines. You might have to cheat a bit and split the difference in the sloping.

Tatts - those cabinets are original to the house (1965) so they settled with the rest of it, unfortunately. It’s not something I thought to check before installing the tile (myself.) You’re right, the small tile probably makes it more noticeable.

If you go through your house with a level, you may find that everything slopes in the same direction: cabinets, counters, floor, furniture. Anything you have hung on the walls (mirrors, art, etc.) using your level for vertical alignment will look slightly “off”. Old homes, yes. A problem, maybe.
Some would consider a 3/4” difference in that small area a significant slope, and that slope may continue all the way across your house. A significant slope may indicate a foundation issue. Is there any indication of cracking or separation at vertical corners anywhere? There is the possibility of having your home lifted back to vertical and horizontal by carefully jacking it up and repairing, reenforcing or reengineering the faulty foundation. I would have an assessment of the issue done by a structural engineer.
Your home is your biggest investment.

Paint the walls/windows ALL with the taupey/gray of the tile.. Don't stare at that corner. What's happening with the fridge?

FYI, you can get solid surface sill material from Home Depot. Siltech is the brand.

By the time that you have your things on the counter no one will notice.

Love you dishwasher!