Thanks! That explains almost everything!
I thing that’s still not solved yet: the artical says “To see all Untagged objects, you can simply turn off the visibility of all tags and folders using the new “Master Visibility” toggle.” My problem that it seems that the active tag stuck and basicly I cannot turn off to view it. That means I cannot turn off the visibility of all tags using the master toggle, and thus cannot display untagged only. And there are a couple of things untagged in my model by design. So there is no way to select them easily.
