Currently, when you add a combo box to the Quick Access Toolbar (such as layer transparency, label font size, or definition query selection), it appears to have been added at first glance, but it disappears when you edit the Quick Access Toolbar or restart the application. Also, some items, such as the transparency combo box, appear to have been added but actually have no effect.
I think it would be very convenient if these items could remain properly on the Quick Access Toolbar and be used. In ArcMap, the toolbar was displayed, so I could quickly access various items. I hope that this convenience will return.