I also made the stairs longer than four metres, but fixed them to the wall with two brackets per section (in addition to connecting the individual sections to each other on the narrow side). In this way, I think you can make the stairs as long as you want. In the case of a support, it simply has to be ensured that it stands really well and withstands influences that can occur at the specific location (child riding his bike against it or a storm raging). And usually "longer" also means "higher up", which is why the cat would also have to be protected against a fall, depending on the concrete situation. That's why I built a section of my staircase as a kind of spiral staircase along the wall, which can then be easily protected with a net. My father laughed at me at the time because he said that cats can balance on anything and that it wasn't necessary. But when my cat got older, looking back, I was very glad that I made the stairs with a slight incline and just secured, because then he could still use them. I hope this answer is helpful.

Yes, exactly, it won't work without fixation or supports. With our 3-metre ladder, it's already a bit unstable.