Magic Mouse will not connect

Let the Magic Mouse charge for a while. Then disconnect it from the adapter or USB port and switch it off.

Then go to your Bluetooth settings on the Mac and see if the Mouse is still in the list.

If yes, switch on the Mouse and double right click the Mouse. You might have to do that a couple of times.

This should connect the Mouse automatically, I just verified that on my MacBook Pro, using my Magic Mouse, which also has the lighting connector.

If this does not work, remove the Mouse from the list again and try to pair it without using the USB cable.

Your Magic Mouse should be shown at the bottom of the list as ready to pair to your MacBook Pro.

Did you already try to remove the Magic Mouse from the list of devices in the settings for Bluetooth in the System Preferences? After that you should be able to pair it again.

Looks like a hardware issue, but I'm not sure, if the Magic Mouse can be serviced by Apple.