With Qt 5.15.5, commit c28dff79721d3805edcd413ef233216b3b3b0104 in Kirigami triggers https://bugreports.qt.io/browse/QTBUG-104983 and all instances of Kirigami.Page lose their scrollbars. Everything is fine if that commit in Kirigami is reverted, or if commit 908aa77d16e00f2bccc0ddae0f8b61955c56a6a1 in Qt is reverted. But with both, Kirigami.Page instances lose their vertical scrollbars.
Note that in many places the bug is completely independent from the kirigami patch. for instance all instances of ScrollViewKcm will use their own scrollview, so will manifest the problem on its own independent from the kirigami patch
also the desktop style is full of references to scrollview contentitems, so working around seems to not to be possible on our end, there is really no other way than a Qt fix for this
https://codereview.qt-project.org/c/qt/qtdeclarative/+/422252
Darn, ok, duping to bug 456574, and let's focus on the Qt patch. *** This bug has been marked as a duplicate of bug 456574 ***