Can nRF52 simultaneously use Bluetooth and act as USB HID Keyboard?
nRF52 has only a device type USB controller, so it is not possible to connect an USB keyboard directly to it.

You would have to use an external USB host controller chip or try something like V-USB (but it will most likely be impossible to use reliably because of the Bluetooth stack timing requirements).

It would be quite easy to interface with a PS/2 keyboard though...