Endless choices…if you search Pinterest for “wood shelf above sink between cupboards” there are lots of ideas. Given what can be seen in your picture, I’d go with a warm earthy feel and test different combos.

Kitchen things that dont get used often. Soup Tureen, Decortive pitchers, plates or platters…..

And keep it simple.

Not every space needs to be filled up.

Install your lighting first. If it's a pendant, chances are good you can put something on either side of it.

Or just use a mirror cut to fit the back space.

What accent colors do you have in your home? I'd add something ceramic in a color to bring some life to the space along with greenery in a bowl or vase to add some softness and life to the hard surfaces.

I'd put something you like up there - I'd do a collection of chunky vintage white pitchers ;)

Agree with la_la Girl. Some white items could be nice with the dark cabinets, dark shelf and the white in the backsplash. Maybe a trio of white pitchers, bowls, vases, etc. Framed art might also be nice that fits the size/shape of the space. You can always just lean it against the wall.

The shelf takes away from the beautiful tile. Not sure why it's needed.

it's pretty dark. too late for a sconce, i would have done the light like this

some type of sconce at the top.

so something in lighter tones?

try to bring in similar elements onto the countertop so it all ties together

I have my collection of teapots on a shelf in my kitchen. But, if you have attractive things only used for holidays, that might be nice.

The pattern in the tile makes a bold statement which is why I mentioned keeping the shelf items simple.

I would remove the shelf. It isn't practical, and it intereferes with the view of your very nice backsplash.

Remove it then see if anything needs to be there with that very busy backsplash

Remove so you don’t have to clean it.

If possible, without damaging anything, I would remove it. I don’t think it adds anything & anything you put up there will be just another thing to clean & having to get that stool out.