Mouse = Bluetooth 3.0
Dongle = Bluetooth 4.0
Keyboard = Bluetooth 4.3 (or do you actually mean 4.2)
While backward compatibility, e.g., 4.0 supports 3.0/2.0/1.0, is incredibly common I have yet to see forward compatibility, e.g. 4.0 supports 4.3, exist. Sometimes, and this appears to be one of them, it need not be a major release number difference to cause issues with compatibility.
The dongle (or internal card) to which all peripherals will be paired should always be running the Bluetooth protocol that is at least as recent as the one run by the peripheral with the most recent protocol.
Edited by britechguy, 17 January 2018 - 11:57 AM.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Presenting the willfully ignorant with facts is the very definition of casting pearls before swine.
~ Brian Vogel