This was lost by the introduction of the default action as the MouseArea steals events from the TextField below.
To address this, selecting text and click handling has been implemented manually. Furthermore, the mouse cursor is changed to an IBeam cursor and turns into a hand when above hyperlinks whose URL can now also be copied separately from its text in the context menu.

BUG: 386118
FIXED-IN: 5.12.0

• Clicking action buttons still works
• Clicking a notification with default action will still trigger the default action. An action without will not do anything, ie. the dialog won't close, just as before
• Clicking a hyperlink will open it
• Click vs select drag feels natural, I implemented it using manhattan length similarly to MouseEventListener
• The cursor is an IBeam over the entire body text area and turns into a pointing hand when ontop of a hyperlink
• Right click menu "Select All" entries select all text, "Copy" copies the text. Ontop of Hyperlinks the "Copy Link" entry copies the hyperlink's URL
• Notification still seems to timeout properly, with or without user interaction, but stays open while cursor is ontop of it

Needs D8445 (ungrab mouse hack) or else after having opened the context menu, you continue randomly selecting text as the MouseArea gets confused as to whether the mouse is pressed or not.

Only quirk I noticed is that while selecting text will scroll down the view as needed it won't work to scroll back up but whatever.