Can't apply keyword, label, or status to multiple documents

I want to merge two projects but also want to keep track which files came from which project, so I thought I would use a couple of keywords to differentiate them.
Won’t work. No matter what I select, only the first doc or folder gets the keyword.
Checked here and saw KB’s response to a similar question. First I reset preferences to default. No joy. Next I simply deleted the app and its associated data folders (with AppZapper) and started from scratch with a newly downloaded app.
Opened a new, blank project. Still doesn’t work. Made a screen recording:
I was originally going to say I know I could use labels or status instead. But then I tried it. SAME THING. I cannot apply either to multiple documents or folders. Just one at a time.
I apologize if I’m being thick and missing something obvious. I have a desktop Mac and will try to do it on that later today.

Update: I checked on my desktop iMac and the behavior is the same: opened a new project, made a few documents, can’t apply keywords, labels, or status to more than one doc at a time.

Both machines running OS 10.14.3 with the latest version of Scrivener (3.1.2).

Select the documents in the binder (use Cmd-click to select multiple). Open the Project Keywords list. Drag the keyword and drop it on one of the selected items in the binder; the keyword will be assigned to all selected items. See section 10.4 of the Scrivener manual.

Thanks. I guess I’ve never had the need to assign metadata to multiple documents at once. I assumed the inspector could be used to change metadata for more than one document at a time.

There are tricky questions about what the Inspector should show you when you pick multiple binder items and even trickier questions about what it should do when you make various “moves” in the Inspector. There is also a serious question about whether allowing certain moves from the Inspector would lead to user mishaps. The by-binder-only functonality on this enables us to make this kind of batch move without raising that issue, because this way you are applying the keyword in a visually explicit way to the group.