the photos are difficult to read.

Don't be afraid of color, color creates interest. Define the angles to make the space appealing. Is the art wall part of the entry/stairway? What are those small doors for? are the stairs carpeted or is it concrete? I don't understand the space well enough to advise, sorry.

So the first picture is at the bottom of the stairs with the entry door to the right, the second is just what you see when you are in front of the door, the third is going down the stairs towards the entry door and the last is at the top of the stairs. Is that correct?

You could do something fun with the stairs themselves. If you removed the carpet you could paint or tile or do something fun on the risers.

https://www.google.com/search?q=fun+risers&rlz=1C1GCEU_enUS868US868&sxsrf=AOaemvLrTTujzCFJ2-wpYMaLqDomTT2q4A:1641327315930&source=lnms&tbm=isch&sa=X&ved=2ahUKEwim2oDd9Jj1AhWrSjABHcABCrEQ_AUoAnoECAEQBA&biw=1400&bih=1276&dpr=1

If that is not an option you could add a runner and also hang some art on the stairway walls.

https://www.google.com/search?q=runner+on+carpet+stairs&tbm=isch&ved=2ahUKEwj4varf9Jj1AhW1wikDHds_Dd4Q2-cCegQIABAA&oq=runner+on+carpet&gs_lcp=CgNpbWcQARgBMgUIABCABDIFCAAQgAQyBQgAEIAEMgYIABAIEB46BwgjEO8DECc6BAgAEEM6CwgAEIAEELEDEIMBOggIABCABBCxAzoICAAQsQMQgwE6BwgAELEDEEM6BggAEAUQHlDOBVjdHWDlO2gAcAB4AIABzAGIAY8YkgEGMC4xNi4xmAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=2KrUYfjxMLWFp8kP2_-08A0&bih=1276&biw=1400&rlz=1C1GCEU_enUS868US868#imgrc=5qlsDIMQ473rCM

https://www.google.com/search?q=art+in+narrow+stairway&tbm=isch&ved=2ahUKEwjF1vj39Jj1AhWLOd8KHRyYDtgQ2-cCegQIABAA&oq=art+in+narrow+stairway&gs_lcp=CgNpbWcQAzoHCCMQ7wMQJzoGCAAQCBAeOgUIABCABDoICAAQsQMQgwE6CAgAEIAEELEDOgQIABBDOgcIABCxAxBDOgQIABAYUN0KWLhBYItEaAFwAHgAgAHrAYgBvCSSAQYwLjE1LjmYAQCgAQGqAQtnd3Mtd2l6LWltZ8ABAQ&sclient=img&ei=DKvUYcWgGYvz_AacsLrADQ&bih=1276&biw=1400&rlz=1C1GCEU_enUS868US868

Looks like gray carpeted stairs & wall art at top of stairs. What I see is stairs immediately in front of you when front door is opened. Looks like a living / sitting room to right which is behind the front door when it’s open. I see a door jamb on left - need pics of that side. Looks like baby or pet gate at both top & bottom of stairs. what rooms downstairs & what's up them? And yes, please tell us what those secret doors are that can be seen from top of stairs! Are you in UK?