Get a Day Bed or a Study Bed, this one is from Pottery Barn Teen. The desk pulls out. Or simply use a separate bed/daybed with a small desk beside it. Paint the area a dark color for coziness. Install dimmer switches and get lamps with bright LED dimmable bulbs that can be adjusted for different uses.

https://www.pbteen.com/products/costa-corner-study-storage-bed/?cm_src=reducedClick

In a room without natural light, artificial light is very important. If the room doesn't already have recessed lighting, consider installing some for overall lighting. Strategically placed lamps for task light are also important.

It's probably the Dining Room. That is a oft-used characteristic in an open floor plan, where the Dining Room borrows light from the adjacent rooms. To put in a study/guest it would have to be temporary (furniture, not permanent walls). For privacy, and separation from the open rooms, screens of some sort.

yes. but I would like to take out some space from the huge dining room area (too big for me) and have a solution for my elderly mom when she comes to visit (once or twice a year? ) Definitely it needs to be a temporary solution. I was thinking also of some sort of screen for privacy and block the minimum natural light that comes in from the open floor plan. any ideas for temporary solutions of screens?

Can you post a to scale floor plan of that whole living space not just this one .

The wall(where the "desk" is) will be longer. the entrance to the big room will be as wide as a door.

Oh...I see. I thought there was a recessed nook as a separate area from the dining room. The area will be in the dining room. Rotate the dining set 90 degrees and move it closer to the living room. Get portable folding Shoji screens that let the light through, are foldable and lightweight to store away. This one is only 16 pounds.

https://www.wayfair.com/furniture/pdp/winston-porter-keitez-folding-rice-paper-room-divider-w004394908.html

Great idea. I like it.

I'm creating a space for my parents when they come to visit and thinking a lot about what is safe and useful. How many other people live in your home? I'm just thinking about what kind of privacy your parent might want or need that a folding screen will not afford. They are also incredibly unstable should your mom ever try to steady herself on it. (Of course nobody would intentionally do that, but reflexes kick in when you are about to lose your balance. It just doesn't seem like the safest thing.)

I'd consider walling off that end space in your dining room to make an office with a sleeping space. You could make it with double pocket doors or french doors with blinds so that there is an open doorway to let light in but it can also be closed off for privacy.

Thank you. I was thinking about it too. I will need clear walls with drapes that I can close when privacy is needed and open when light and spacious feeling is needed.