It is not possible to paste selected text by middle mouse click into Qt5 apps, for example, kwrite. It is possible into gedit for example.
Pasting works on Xorg, but not on Wayland.
Pasting also works if I start application with env QT_QPA_PLATFORM=xcb.
Thanks, adding that env var was a great temporary workaround for me.
Indeed, Qt5 does not yet support gnome's primary selection protocol yet, https://bugreports.qt.io/browse/QTBUG-66008
*** Bug 1770057 has been marked as a duplicate of this bug. ***
Will come with Qt-5.14 (or newer)
Works on Fedora 38 with Wayland too.