Why don't things expand automatically when set to?

Version 4.21

I’m struggling with the UI system currently. My mental model of flow containers comes from CSS Flexbox.
When creating a VFlow with children, the default cross-width is 0 instead of the parent width, which makes no sense to me. The Horizontal Container Sizing option to fill appears to do nothing.

Nothing I try makes it expand except setting a minimum size which isn’t responsive.

Is this still being worked on or am I doing something wrong?

Containers don’t expand unless they have non-container children afaik. So just add any child object like a label or a panel.

The one exception, at least in my case, seems to be GridContainer. For that, it seems either custom size on the grid container itself OR each of its children is needed. Maybe I’m doing something wrong, though.

If this doesn’t help, describe your hierarchy exactly (ideally with screenshots of settings) and under what conditions you’re running into a problem.

I’ve tried HFlow containing GraphEdit and VFlow (each with children of their own).
I also tried reparenting to panels, that just created a huge mess. It doesn’t solve a problem because you want the panel’s child to also fill it (meaning it has to be a container).

It doesn’t seem like the system has been thought through very well, at least in UX terms