Honestly, the stair tool kinda sux. I mean I like the idea but would like to have the legacy option at my disposal as well, as sometimes it can be very frustrating to make a stair with the new tool, especially if you want some exact design. I myself have several times resorted in those special cases to modelling the stair using other methods, riser by riser, rather than messing with the needlessly complicated stair tool. But it's serviceable for a quick stair while making a study I suppose.
From Archicad 8.5 all the way to the present. Passionate Autocad hater as well. Wish to save palets and menus individualy in work enviroments: https://bit.ly/3pg3Bx7
I agree with you @Jan Vlach there are limitations with what the stairs can do don't get me started with stringers. it doesn't allow you to do certain things need to like do parts by parts to get the look that you want. 😐
In the end what is your Objective? ArchiCAD 9 onwards