"Should it be" ???

There's no should. It should be something you enjoy seeing. It can be a vertical piece, it can be a stack of prints hung vertically ( use three ) and beyond that it's a mystery as we have no clue what you may like LOOKING at.

You know you, go shopping.

Take a look at Etsy.com or shop your local decor stores for ideas on what you'd like to see there every time you enter the kitchen. It's a personal choice. I would get some fun quirky framed art like 12x12 and put together there.

If it were me I’d find a few smaller pieces I loved and stack them (I am a sucker for vintage transferware platters bc I like some patina in the kitchen but that’s just me)

Paint it the exact same color as the cabinets.

Doesn't need anything.

Maybe a vinyl wallpaper if you really want something there.

Not a place for art given the 'fridge' door. If it were me I would get a large magnetic calendar/menu board going. As said this is a very personal choice. The idea of shopping for art I find confusing. In my life I find things I LOVE and then find a place for them in my home. I would leave it empty until you happen on that piece. I want what I look at to be more than something that had the right size/shape/colors in it.

Great place for art. I too have a galley kitchen with simple colors and it is nice to have a focal point.

I'd hang three vertically stacked plates or platters. But first you need to check the door swing of the fridge and make sure you don't bash anything that will be hanging. If it is a problem, hang textile pieces - like three interesting pot holders, or woven trivets, instead that you are sure you can pop in the washing machine or wash well by hand, as they will certainly get dirty.

You can always hang from a dowel a beautiful French dishtowel.

Or vertically hang two matching towels.

I like the selections here .https://www.yvonne-estelles.com/collections/towels 

Food art in a palette and subject you like.

"Still Light" Original Artwork By Gretchen Trees · More Info

Check out society6.com for framed art in many subjects and sizes. Or museum for food related still lifes.

Contact a local high school artist to paint you a custom mural based on things you like. A friend of mine had such a wall done in the flying monkeys from Wizard of Oz.

Agree with Jan. It has to be something you enjoy looking at. Also, take into consideration the fridge door swing as well.

The hand paint works too! Whimsy is fine, a view is fine, and nobody here can tell you what speaks to you. But I absolutely understand your desire not to be staring at a "dead " wall: ) of paint on drywall. I'm a no on that.

What do you like? How much do you want ( or can ) spend? For very reasonably priced art check out Desenio Art, poster style, search for ”kitchen” art , they have 322 choices. You can select size,, frame , etc. I like to use brown wrapping paper in varying sizes to help visualize layout ( if multiple ) & size. Aside from that ,I like Jan’s idea.

I would do a trompe d’oeil, an amusing visual illusion playing on the geometry of the space.

. . . using Minardi’s process.

Faux window

This brings together the gray of the floors and the cream of the cabinets. https://a.co/d/1DPRevv 

I never reccommned any art to a client . I would look for something vertical and please at least change that lighting to a LED track light

I’d add a vinyl runner to add some interest and personality and you could even paint that wall a comp color in the mat, to create more of a feature wall.

Look for a poster, prints, drawing or photo that resonates with you, but before buying anything, be sure to tape out a few sizes to get a better sense on how you want the space to feel.

A wireless Samsung Pro Frame tv can be mounted in portrait orientation. Unlimited art choices. Snazzy Labs has a YT video with a review. 2020 32" and newer. All sizes 2022 and newer. Get one off FB Marketplace.

If you choose to consider the suggestions above about changing the ceiling light, you could also consider an LED grow light aimed at that wall and grow some live plants, herbs, violets, or microgreens in shallow planters in that space. Your sink is so convenient there for easy maintenance.

I support the fresco idea. You could choose something with perspective (a landscape) and in softer tones.

How about covering that end wall with a translucent acrylic panel with diffused lights behind it, that you can change from warm evening to bright day. An erasable marker and you also have a whiteboard for grocery lists and, you know, art.

This kitchen always comes to mind when galley kitchens are mentioned. Maybe consider tiling the entire back wall?

I'd select a paint color for the far wall that is darker to contrast your other finishes.

I'd change out the ceiling light fixture that provide less garish quality light

Select whatever art you like that inspires you in the kitchen.

IMO it needs some color; what's your favorite one? What colors are in the rooms at the other end of the kitchen? I think a wallpaper in the colors you love would be nice. I like the botanical print @JAN MOYER posted; here it is in your kitchen.

For fun, I took a color from the wallpaper and painted the wall by the window and added a light.

I love Jan Moyer's idea of a wallpaper mural at that end of the kitchen!

For a general idea of size, I prefer the first.

If you have the funds, I think it would look better if you tiled the whole wall. It looks somewhat disjointed where the tile stops. Cute little kitchen though!

24" x 60"

I really like your flooring. Would you be willing to share the brand and name? Thanks!

s y, The floor is from Porcelanosa. They have an incredible selection.

Thank you, appreciate it.