I just saw this myself. There’s a thing in the view menu called “Show Tab Bar” (right at the top). This presents a second “level” of tabs. The close tab command works on that one.
As far as the tabs I’m used to – the ones that show the current note name and have a view icon – I don’t think there’s a way to close them with the keyboard.
I don’t understand the purpose of the two levels of tabs, but seeing as I’ve just learned about them, some experimenting is in order…
IF you have two levels of tabs… and these are different from the tabs you get if you “open original in new tab” or use the “+” or “new tab” functionality.
Just happened on this thread. I also see the value of closing tabs. I often navigate through my notes by opening the original of an alias in a new tab or using URL to open a particular view of a particular note. Over time tabs accumulate and I need to close them and something like ⌘-W for TBX tabs would be very welcome.