$ dbus-launch --version
D-Bus Message Bus Launcher 1.12.16
Manjaro is based on Arch, and as such is a rolling release, so there isn’t really a version number. I am up to date as of this morning.
But I think I figured out something that will work, it’s not a 100% fix, but it’s a decent workaround. The primary issue seems to be that when KDE starts it has trouble with making/attaching to a dbus session. With 5.17+ it seems to expect a session to be present to attach to. A little more research indicated that for users, systemd should create the session on login. So I updated /etc/pam.d/nx to include the same content that is in /etc/pam.d/system-local-login. Now KDE works when I login via NX.
The drawback is that a user is supposed to have only one “session”–if you login via GUI and then ssh to the same machine as the same user, you should be attached to the same session in both places. This doesn’t seem to happen–on my Debian Buster machine with KDE I only have one session when NX and ssh’ed in. On Manjaro I have two sessions.
Or maybe I’m mistaken and two sessions is the right behavior and Debian is not working right.