Honestly, now that container queries are available, I see very little use for breakpoints. Container queries allow for easy reuse of components, and a truly fluid and responsive design.
You're still probably going to want the left sidebar of your multi-column layout to collapse behind a menu on narrow viewports and abruptly appear when the viewport width gets to >= n [0]. But it's conceivable that the value of n emerges from some constraints you specify (such as the minimum desired width of the sidebar and the main content column), instead of being chosen upfront from a small list of predertmined breakpoints.
[0] E.g. https://tailwindui.com/components/application-ui/application...
The example you give of a sidebar collapse with a menu button replacement can easily be accomplished with a container query on the wrapping box, no?
I'm honestly curious about a use case that a media query breakpoint can handle, but which a container query can't.