In the Keybase menu on MacOS is the standard hide application item Hide Keybase item with the hotkey 鈱楬. Selecting this item in Keybase 5.1.1-20191211223249+15bbb94c23, on MacOS 10.14.6, shifts focus away from Keybase but doesn't hide it. The window stays front and centre, while focus shifts to the next application in the stack.
Indeed it is broken again. There is some sort of regression.
This is still broken :(
This is still broken in 5.4.0 on 10.15.4 :(
This is still broken.