IOS – use the Mac keyboard as input to another Apple device

Is it possible to use the native keyboard on one Mac, to control the keyboard input of another Apple device, especially another Mac?

And so doing, without having to completely redirect the input device, i.e. disconnecting/connecting a Bluetooth keyboard to switch it between devices.

In my setup, I have a MacBook Pro and an iMac. Ideally, on the MBP, I would like to press a keyboard command or an GUI icon to connect the built-in keyboard as input for the iMac.

^{Note: Screen sharing is not a viable answer for this question.}