Not enough to go on! Show us the surrounding spaces, describe your style, etc. There are many ways to go (including closing it up so you can hang larger art)!

Possibly a mosaic tile, or Mediterranean style depending on your homes architecture. Wallpaper would work or a hanging metal sculpture. I always love an oil painting too. An ornate mirror with small console below. It's charming but not very deep!

mirror in same shape as the niche, narrow tray on ledge for keys - maybe, or nothing on ledge.

I need to see the whole space but usually if you have to ask the best soulution is to close it up and then deal with the space with no niche. BTW i don’t even like shower niches so IMO cover it

Cool Mirror, Art, Shelves. Type 'entry niche' into pinterest and you'll see many ideas.

As it is an entrance niche and the wall color is dark. using indoor planter and medium sized show piece will enhance the entrance. using greens and golden or any very dark colour. and you can hang some handmade hangings at the center.
using mirror will make it look bigger but not really good suggestion. u can hand mirror artwork or simple round mirror on the blank wall next to the niche.
i hope it helps.

Seriously...I would get a large piece of art and hang it over the hole.

It would help to see more of the space. I would highlight it as suggested so well in previous posts. Any front hall need a landing spot for keys, etc. A small bowl or wooden box would work. Lots of options.

Thank you guys for

all your responses. I recently moved in and haven’t had enough time to figure out the decor of the space. Sorry for the lack of details, I know better lol! My style is contemporary and simple, usually go with metal finishes, abstract decor. Hope this helps!