Hmmm, well this is the XDG-* packages I have installed:
$ pamac search --installed xdg
[...]
xdg-utils 1.2.1-1 extra
Command line tools that assist applications with a variety of desktop integration tasks
xdg-user-dirs 0.18-2 extra
Manage user directories like ~/Desktop and ~/Music
xdg-desktop-portal-kde 6.3.3-1 extra
A backend implementation for xdg-desktop-portal using Qt/KF5
xdg-desktop-portal 1.20.0-1 extra
Desktop integration portals for sandboxed apps
xdg-dbus-proxy 0.1.6-1 extra
Filtering proxy for D-Bus connections
Well, I do have gtk3-nocsd-git installed:
$ pamac search --installed nocsd
gtk3-nocsd-git 3.0.8+2.r84.20221015.a356bf7-2 AUR
A LD_PRELOAD library to disable gtk+ 3 client side decoration.
And I’ve got this environment variable set in /etc/profile.d/environment_variables.sh (self-created file):
export LD_PRELOAD=/usr/lib/libgtk3-nocsd.so.0