I have a 2011 iMac with Bluetooth 2.1, and recently purchased a Bluetooth 4.0 USB dongle required for my new wireless mouse.
The dongle works great - I paired my mouse and keyboard to it without issue and used the following terminal command to ensure macOS uses the dongle instead of the built-in 2.1 module:
sudo nvram bluetoothHostControllerSwitchBehavior=always
However I've noticed when I reboot or shutdown my Mac the login screen doesn't respond to any input from my wireless keyboard, so I can't enter my password to login. After logging in (using a wired keyboard) my wireless keyboard and mouse work perfectly fine. I suspect this is because I have FileVault enabled and the USB dongle's driver is not loading at boot?
It seems to me the best solution would be to leave my keyboard paired to my iMac's built-in module and only pair my mouse to the USB dongle, since I can login without needing my mouse, but I can't seem to find a way to use both Bluetooth modules concurrently. Is that possible?
Alternatively, is it possible to configure macOS or my iMac's EFI to load the USB dongle driver at boot? Replacing my iMac is not an option for me at this stage but I'm open to any other alternative ideas too. Thanks.