cmd + w should close the window (but not quit the app) but at the moment it seems not to be doing anything
Hmm I’m unable to reproduce this. Do you maybe have another app running that may be taking over that shortcut? If not I would try reinstalling the desktop app to see if it persists.
Thanks 
Ah that’s weird that you’re not getting it too! Happening with me on two computers. Just noticed that cmd + w works at closing the tabs of open files but doesn’t close the main opening menu of “recently viewed” or other options in the side bar. I’ll try a reinstall.
Cmd + W doesn’t close the window, it closes the tab, and you can’t close the main tab. To close the window, press Shift + Cmd + W.
That explains it, thanks Gleb!
It’s a shame that it’s intentional because that seems very unintuitive to me. I can’t think of any other application that doesn’t close the window with cmd + w.
Usually applications with tabs close the tabs sequentially with cmd + w until there’s only one left, then one more cmd + w closes the window. E.g Finder, Safari, Chrome, Firefox, VSCode, Atom, Terminal, Hyper