Do you already have a dark strip bordering the countertops?If adding white tile with dark grout you may be over emphasising that section and making a striking and unintentional eye pop.
Tile will be nice at same height as cabinet bottoms.
Mock up some samples and view over a few days before making a black /white op art eye catcher.
YMMV!

I would go a quarter up the window.

Quarter of the way up the window. Have you looked at inspiration pics of black grout on white subway tile? Are you sure that is the look you want? I think it will be busy and make your kitchen look smaller. I'd do white grout or if you really want a bit of emphasis, very thin line medium grey grout.

IMO a line under the cabinets and the sameon the waal of the dark material is going , under the windo I think part way up the window looks like you ran out of tile I do hop that thin line

I wouldn't add tile. You already have a short backsplash. Enough for everywhere except behind the range.

More is not always better.

Bottom of cabinets.

But I’d strongly reconsider the black grout. Like kendrah said, to me it sounds too busy. There’s a houzz ad that often pops up for me where a bathroom is white tile with black grout. Not a fan.

I’d also strongly consider removing the backsplash. Tile on top of backsplash is a lot, as JH says.

Finally, though it may be a challenge with the existing cabinetry, it doesn’t look like it would add many square feet to go full wall. I love that look - with white grout.

I had not noticed you already have a little black splash. How many inches tall is it?

What material is your counter top? Does it have a bumpy surface?

I didn't notice it either, I was focusing on the red line.

I would take out the existing black backsplash if I use tile. The countertop is Dekton. I forget the exact name of it. It has a slight texture to it. Reminds me of slate.

I would go half way up the window as your photo shows. As for the black grout; a skilled installer and good tiles are a must. The grout color will show all the discrepancies in how tiles were laid and any imperfections of the tiles.

I had ChatGPT add tile into a couple photos. It took a while because ChatGPT isn't good at duplicatings images. It always changes things you tell it not to. But the images it created gives me a good idea of what the tile will look like.

One with white grout

I would go up to the bottom of the window. Remove the short black backsplash. No black grout- it would be too busy.

I like the the second picture ( quarter way up the window) and the light gray grout.

Black grout can be a great look or it can be a mess. It looks good with tiles that are fairly uniform and straight. Tiles that can be laid with minimal grout lines. Anything handmade or with uneven edges will require fatter grout lines that can bleed into the tile. Not good. Also don’t use black grout if you’re using crackle tiles, you’ll get the same bleeding and it will look awful.

Your short backsplash is nice but won’t work with tiles above it. Either continue the countertop material as a backsplash or replace the short one with tile.

Or leave it as is.

I just wonder when the black backsplash is removed, how the surface underneath looks, being that the counter is polished. Is it polished but topped with glue that comes off easy or is it unfinished? How is it fixed to match the rest? If it'll look different or be expensive to fix I would have no problem leaving it and adding tile above it, I have seen that done before and it looks fine to me.

I'm pretty sure the backsplash is glued to the wall and has caulk to seal it along the countertop. I've wondered about that too...if the backsplash scratched the countertop.

I like the mock up that chat GPT did running the tile all the way up to the ceiling. It doesn't make the room so choppy that ending it early would do. Rebecca Robeson, an interior designer recommends running the tile on the entire wall and I agree that would make the space look bigger and symmetrical and a good flow. Light gray or white grout please