Manjaro cannot prevent all issues getting to stable branch
Sometimes the best that can be done is to have information posted in Known issue and solutions section of update announcements so users can resolve problems when they occur
Gtk4 support for pamac GUI was first announced in unstable branch 21 Jun 2023
Known Issue and solution was first posted in [Testing Update] 2023-06-24
pamac-gtk
11.0.1 uses Gtk 4 that is not supported by Xfce
user can replace pamac-gtk with pamac-gtk3pamac install pamac-gtk3
Solution was reposted to [Stable Update] 2023-07-10