same color and style so it looks intentional not an impulse add.

Here's a quick visual. Make sure the door opens into the hallway and not out over the steps. (That would be a building code violation in the U.S.) If space allows, adding wing walls beside the steps would make that area look more finished/intentional. (Can the refrigerator--if that's what it is--still open with an added wall on that side?) And a wall section will need to be added over the door, of course.

The same color as what you have. But I suggest full view with the brown wood...brightens both the hall and kitchen.

I assumed your goal was privacy from the living areas for those using the hallway (bedroom to bathroom), but if not, @oncape's suggestion offers another option. Or use obscure glass that lets light through but not views.

Imo the brown color of doors is way too harsh and overbearing with the light walls and floor. I would paint the doors a complementary taupe color such as BM Pashmina. I would install a new door with full translucent glass ( no grills) and paint same color Simple side rail on either side of steps painted same color as doors, rather than partial walls on either side. Railing will give a lighter more airy look

With dark door and simple railings (still think the tiled-box steps need something to finish off the sides):

Here's chatgpt's version with a light door:

I don't much like chatgpt's railings (plus it didn't align the left one correctly).

I personally like the contrast of the dark door, but it's hard to be sure which is better without seeing the whole space.

Agree with going with same tone as existing doors.

much airier looking

again, both railings not lined up properly but you get the idea

Suggest black double paned glass doors as I think they will be flattering (open or closed). Can only see one railing fitting on the right as you enter, given the fridge’s location.

If you want more privacy, this style stained to match the others would be nice as well.

If interested, consider improving the lighting, add a longer runner and even some art.