I want to use dunst for notifications, but when i try to start it, i get this error:
CRITICAL: [dbus_cb_name_lost:1153] Cannot acquire 'org.freedesktop.Notifications': Name is acquired by 'Plasma' with PID '1589'.
Any help?
Hi - I don’t believe software like dunst is generally designed for full-featured desktop environments like KDE Plasma, GNOME, etc., but rather with more minimal configurations using a standalone window manager: Desktop notifications - ArchWiki
Searching around that project’s issue tracker might lead to some possible workarounds, but on the face of it they seem likely to risk breaking something else.
You might be in Here be dragons territory here 
Definitely Here be Dragons territory.
The way to make this work is make sure that your desired notification service is running before plasmashell starts up. So start it and then restart Plasma.
But, again, Here be Dragons. I would recommend not submitting bug reports about weird interactions because what you’re doing is only supported on a technical level, not a “we want to offer support for it” level.