The cantilever staircase does not hold, the stair builder is not a staircase builder

Pictures of the whole thing would be interesting. Normally, everything sticks to a concrete wall.

It's not about shifting responsibility onto the state. Of course, I made a wrong decision and learned from it. But in a constitutional state, there should be mechanisms to take action against poor performance or false information. Otherwise, unscrupulous craftsmen could continue unpunished.

You do have rights (for example, the Building Code regulates such a case). You just have to sue for them in an emergency. I have already told you how that works.

Have you demonstrably requested remedy of the defect 3 times with a set deadline (preferably in writing)? All 3 attempts have failed.

Therefore, in my opinion, you have the right to withdraw from the contract and claim damages. You can now commission a contractor of your choice to create your staircase free of defects. However, you are also obliged to minimize the damage.

How did you determine that the steps don't hold?

As I said before, I would be happy to receive photos and/or plans.

I can't imagine that an anchorage in the concrete does not hold. Is this a structural defect?

What does your construction manager say about this?

In my opinion, you therefore have a right of withdrawal from the contract and a claim for damages. You can now commission a contractor of your choice to build your staircase free of defects. However, you are also obligated to minimize damages.

The only but significant problem, which must be carefully considered, is "being right and enforcing the right."
Depending on the scale, I would think more than twice about commissioning a new contractor at my own expense (!) to build and/or install the stairs correctly. If necessary, I have to recover the money through legal action. Until then, quite a few small craftsmen have already hit a wall and thrown in the towel.
Get the money back first and then reassign.

First get the money back and then reassign.

If you have the time, exactly like that. I suspect that the entrepreneur will not want to pay voluntarily or, worse, will not be able to.

If you have the time, exactly like that. I suspect the entrepreneur will neither want to pay voluntarily nor, worse, be able to.

You find that out quickly. Lawyer, check whether requests for defect rectification were correct, terminate the contract, set a short deadline for repayment (in whatever amount is appropriate), apply for a payment order. Then you have a) certainty whether he will give in or not and b) at least very quickly a title for payment (yes, if necessary, it may also first have to go to court). Whether the title then actually leads to money is another question. But if you can get to the account or once can send the bailiff, that might help.

I cannot imagine that the OP will find someone to fix the botched work. The correct solution is to reassign the contract. To a professional company and claim the additional costs as damages.