With a standard Manjaro Gnome install, I would expect the package gnome-remote-desktop as it is part of Gnome 40 and provides RDP support for Settings > Sharing > Remote.
When users follow the current instructions to enable RDP (because a UI update is still pending), they will run into the issue of the missing package and gsettings schema:
Luckily, this package can be installed via Pamac. But I do wonder why it is not included by default?
It’s included in the gnome package group and is an optional dependency of gnome-control-center. I wouldn’t call that “missing”.
Thanks for correcting me. I am just an end-user.
As a Gnome user, I would expect it to be part of the default Gnome experience… that’s why I perceived it as missing.
Still it seems quite trivial why it is not included, but for example the X11 Gestures extension is included (not optional), even though Wayland is used by default. 
I would expect that package to an optional dependency. In addition to that, there is a Wayland alternative to X11 gestures available.