Thanks for the follow-up - you're right. Column resizing is currently only possible via the header dividers, so a ListBox with HasHeaders = False has no way to resize its columns with the mouse.
I will add the AllowColumnResize property you suggested to both the desktop and Web ListBox. It doesn't exist today (resizing is always enabled when headers are visible), and it will default to True so existing projects aren't affected. I've logged it here: https://feedback.objo.dev/feature/1576
I'm going to pass on making columns resizable by dragging cell borders when headers are hidden, though. The Avalonia grid control the desktop ListBox is built on implements column resizing as part of the header itself - the cells have no resize support at all - and that's the norm for grid controls (WPF, WinForms, macOS NSTableView and Xojo itself all work this way; it's really only spreadsheets that resize from cell borders). Hand-building a second resize interaction on top of the cells would mean custom mouse handling that has to coexist with cell selection, editing and drag reordering, and I'm not prepared to risk the janky pointer behaviour that could introduce.
If you want resizable columns without header text, leave HasHeaders = True and set each column's header text to an empty string. You'll still get a blank header row with working dividers.
