Audio MIDI Setup - the "-" is greyed out?

I have been experimenting with microphone set-ups. In the process, I created a few aggregate audio devices in Audio MIDI Setup, as well as having multiple duplicate microphones. AT one time when I first started doing some recording over a year ago - you could simply click the "-" and delete a device. Now - that is no longer available. Why?

I have reason to believe that the duplicates and extra devices listed now is creating an issue with setting up my podcast recording environment.

I have watched a few youtube videos and read some unhelpful threads here in the community - and none seem to offer a working solution. From opening Library/Audio/Plug-Ins (none of the listed devices show there), to the repeated "just click the "-" in Audio Devices...

Nope - I am the owner of the Macbook Pro - and am the administrator. Seems a rather UN-Mac-like experience.