"Requestor Chat Popover" is marked as an internal component which means it will only show up in UIB if you have maint access. You'll see this on this record /now/nav/ui/classic/params/target/sys_uib_toolbox_component.do%3Fsys_id%3D6030631316e2dd11d17711ed9fd99971

The "Flexbox" and "Grid" Layouts are both simple containers.

Thanks,

Kevin