We (Autodesk AutoCAD for Mac team) have a search box that popups a QTreeWidget to show the search results when the user types in the search box. After upgrading to Qt 5.15 from 5.12, we can no longer click to select an item from the list of the QTreeWidget using a mouse or a trackpad. (Select via keyboard works as usual.)

Here's how we setup the event:

//m_pPopup is a QTreeWidget

connect(m_pPopup, SIGNAL(itemClicked(QTreeWidgetItem*,int)), SLOT(onItemSelected()));

Here's a screenshot of the control: