How to loosen the wooden stair stringer like the fastening?

Hello everyone. I have a stringer made of wood on the staircase that I would like to remove. Ideally without causing major damage, but I do not understand the fastening method and how I can undo it. I hope for your input on how I can solve the problem. See photo. Thank you very much and best regards

I would suspect that you can see a screw with a cover cap there and a washer. Try to see if the round piece (cover cap) can be pulled off. Underneath, I would then suspect a screw.

I already tried that, even with raw force using pliers but nothing happens. Neither turning nor pulling nor levering.

Looks like it's riveted or something. :confused:

By the way, the [Wange] is attached to concrete

I’m guessing stair screw or tension band screw. They are long. Sometimes only the angle grinder helps.