let me demonstrate what I was talking about in the previous reply first. CSP has a special kind of ruler that lets you divide things evenly shown by the purple lines here, so as we can see here when we connect the corners we find the center of the square:
when I distort this into perspective, our center clearly no longer lines up with the halfway point of the line. But the corner method still works to account for the distortion.
ergo, if we want to divide something in perspective, we cant just use a ruler, so instead we use the corner method.
So then what are all the lines I drew here about?
Connecting the corners once will divide it in half, if you do it again you split that into half which gives you quarters, and if you do it again you will have eighths, and so on and so forth.
So if you want 8 stairs, you connect the corners and divide it in half three times over:
Which then gives you the outer edges of your steps and you can draw the rest of the staircase from there.
If we wanted 12 or 9 stairs, then we would first divide it into thirds:
and then either divide that in half until we have 12, or divide it into thirds again so we have 9.
maybe you want to do like, fifteen or something though, so heres how to divide a section into fifths:
you can get 15 by dividing into thirds, then dividing those thirds into five. you can also divide something into sevenths but thats really complicated and not something ive ever needed to do personally ive honestly never even used the fifths before, but theres a video which walks through that here.
additionally, it is also possible to evenly extend things further by passing the line through the center to find the opposite corner
Visually these look complicated, but all you are doing is connecting corners together and making lines intersect.