pkgsrc/misc/qt6gtk2/files
..
README

+----------------------------------------------------------------------
| GTK+2 initegration plugin for Qt6
+----------------------------------------------------------------------

To enable the qt6gtk2 plugin, set the QT_QPA_PLATFORMTHEME environmental
variable as follows:

export QT_QPA_PLATFORMTHEME=gtk2

Place this inside your ~/.profile and re-login for changes to take
effect. 

NOTE: Environment variable QT_STYLE_OVERRIDE should be removed before
usage.