If you need the storage space, you can build a shallow set of shelves in the openings between the joists. My BIL built one for me in the bathroom — it’s lined with paneling, framed, and I had glass shelves cut for it.

Cover with a painting

Art is a good idea

Shelves or a cork board for family photos

What, if anything, is "built in" on each side of the pass through?

How are you using the space on each side of the pass through?

Is that the pass through from which you've removed the shutters?

Is the other white louvered panel pair a doorway with a step down? Is this room a den that was once a porch or garage that is a step lower than the kitchen?

If you have no cabinets on either side or are not leaving cabinets on either side, and if those white panels are "saloon doors" to a doorway, consider whether or not it would be practical to open a wider space and add a sliding glass patio door between the two rooms -- would that be useful to help you control heat exchange, enabling you to warm one room while leaving the other less warm?

If you have a base cabinet on either side of the pass through, would it be useful to you to add an overhead cabinet with a door to the cabinet on both sides to make it accessible from either room?

Out of the picture but I have accents with Buffalo check black and white curtains and pillows. ❤️

Art on the more formal side is a great idea. On the less formal side -- ?kitchen? -- you might consider a cork board or add chalkboard paint for that one side or frame a piece of metal for holding decorative magnets for messages. If there is a kitchen on one side, the niche space might be a good place for a calendar and/or running grocery list. Hope it has all turned out well.