ᐅ How to detach a wooden stringer and its fastenings?

Hello everyone.
I have a stair stringer made of wood that I would like to remove. Ideally, I want to avoid causing significant damage, but I’m not sure how the fasteners are fixed or how to loosen them.

I’m hoping for your advice on how to solve this issue.

See photos.

Thank you very much and best regards

I would assume that there is a screw with a cover cap and a washer underneath. Try to see if the round piece (cover cap) can be pulled off. Underneath, I would expect to find a screw.

I already tried that, even using brute force with pliers, but nothing happens. Neither turning, pulling, nor prying works.

It looks like it's riveted or something. 😕

By the way, the wall panel is attached to concrete.

I’m guessing it’s a stair screw or a tension bolt. They are long. Sometimes only an angle grinder helps.