Screed in 4 rooms is 1.5-2 cm too high.

But it means custom size, in case of doubt then no off-the-shelf doors.

Means special size

...or plunge circular saw with guide rails. Was more than enough for exactly this purpose during the renovation of my colleague's house. If the doorknob then hangs 2 cm lower like here, that's certainly still OK.

You cannot always simply shorten all doors to the desired size. Depending on what kind of doors they are, it is possible, possible only up to a certain size, or not possible at all.

last stage with more strength or just a bar

I would never do something like that voluntarily. Even a single centimeter is massively noticeable and, in my opinion, significantly increases the risk of accidents.

I would never do something like that voluntarily. Even a single centimeter is massively noticeable and in my opinion significantly increases the risk of accidents.

So what solution are you advocating for?

Either accept the 1.5 cm on the doors (in my experience, in old buildings no one catches on them, whereas the "wrong" step, which I know of with a similar height, still causes people to lose their footing) or have the staircase completely adjusted.