Unfortunately libhandy 1.2 won't have a mobile switcher for
Bar have landed just a few weeks before the UI freeze, so it's either 1.4 or something in-tree in kgx.
Me and Tobias prototyped a thing yesterday:
It needs GNOME/libhandy!738 (closed) and will also need a proper API in
HdyFlap to expand the child but leave N pixels. Right now the prototype is just using a fixed height sheet, that's not great.
Later in GTK4 we can switch to a more elaborate design such as a "mini-phosh" carousel or a grid with previews: