An unnumbered page with a deliberately very long title so you can see how the sidebar wraps onto multiple lines instead of stretching

This page has no order:, so it carries no number and sorts after all the numbered items in its chapter. Notice in the sidebar that its long title wraps neatly onto several lines while the sidebar keeps its width — exactly the behaviour you asked for.

Unnumbered pages are perfectly normal: use them whenever a chapter has a page whose position doesn’t matter.