How can I use this wasted space?

I don't know exactly what you're looking for, but here is a link to what we did with our foyer which is very similar to yours. https://www.hometalk.com/diy/entryway/foyer-makeover-remodeling-mess-to-entry-elegance-8688806

Bland Split Foyer Entry to WOW Wall of Thrift Store Mirrors.

Add a shelf above the door to break up the large wall space in a two ...

https://www.pinterest.com/pin/23573598022878687/

You could purchase & install a wall size mural, like wallpaper but with a light scene, such as outside in the spring. That way there is no dusting but it different than just a paint color or you could stencil a pattern. Just Google wall murals, you’ll find many

Perhaps you should invest in having cabinetry built for that area for storage with closed doors. It certainly will keep your dusting to a minimum and could store very rarely used items. Sadly it may very much close in the area but will assist with your negativity about dusting shelves etc. that you've expressed for the two other's ideas. Good luck!

Hi there,

Use a feature wall of wallpaper!

How about something like this? https://society6.com/tapestries

Or this? https://society6.com/wallpaper

You are pretty much going to have to do one wall as an accent. You can paint it in a color that you love, but maybe wouldn't want in the whole room. You could also then stencil a pattern of your choice over it if you like. This is not very hard. Wallpaper is also a possibility. Either way it would add some color and drama to the space (you could go bright or subtle). Now if there was only some way to keep those cobwebs out of the corners!

Hi, Joann,

Unless you can extend the floor over this open area, your only option may be shelving, which will result in awkward dusting and tax your physical limitations.

Perhaps a structural engineer can better advise you.