What has this to do with wayland or XFCE? The only major DE that is using client side decorations is gnome. This has been true since 2018:
> I heard that GNOME is currently trying to lobby for all applications implementing CSD. One of the arguments seems to be that CSD is a must on Wayland. That’s of course not the case. Nothing in Wayland enforces CSD. Wayland itself is as ignorant about this as X11. [...] In fact we created a protocol (supported by GTK) that allows to negotiate with the Wayland compositor whether to use CSD or SSD.
> I heard that GNOME is currently trying to lobby for all applications implementing CSD. One of the arguments seems to be that CSD is a must on Wayland. That’s of course not the case. Nothing in Wayland enforces CSD. Wayland itself is as ignorant about this as X11. [...] In fact we created a protocol (supported by GTK) that allows to negotiate with the Wayland compositor whether to use CSD or SSD.
From https://blog.martin-graesslin.com/blog/2018/01/server-side-d...
Wayland is agnostic, and it's up to the compositor and application to decide what to do while operating under wayland.