Hi,
I just want to add my experience to how I solved my issue with the Bluetooth Setup Assistant popping up and making it impossible for me to use the mouse or the keyboard on my Macbook Air 2018 for a minute or two.
Whenever I would ''not'' have a keyboard or a mouse connected to my Macbook Air the window with Bluetooth Setup Assistant would pop up to search for Bluetooth devices and render the computer useless for a good two minutes.
Having the Bluetooth Setup Assistant popping up can simply be turned off by following this path:[br]
- System preferences > Bluetooth > Advanced > Uncheck the top two boxes and click ‘OK’
I hope someone can benefit from this, though it turned out to be very simple to fix.