My Buetooth keyboard connected fine, but the iMac refused to acknowled the existence of the Magic-Mouse2. After reading a substantial number of posts with no success, I tried the following, with positive results. However I have yet to reboot my system. (iMac Retina 27" Late 2014 with Mac OSX 10.15.4) I disconnected ALL Bluetooth devices, keyboard and Magic-Mse 2 (MM2),& rebooted 4-5 times, with Bluetooth turned OFF. To navigate the screen I used my B&W 2008 iMac mse. I rebooted again with MM2 connected by cable to the computer, with MM2 turned OFF. I then turned on Bluetooth and located MM2 in Bluetooth window. Next I turned on MM2. Bluetooth recognized MM2. (it was the only device connected, since the keyboard was still turned off.) I then reconnected the keyboard via blue tooth, as per Apple's instruction in the HELP Menu (Connect an Apple Wireless Accessory ...), and it worked. So far, I have a functional mouse and keyboard, therefore, so far all’s well. I’m afraid to turn off my system. - If it does not reboot as it shoud i shall repost, and hopefully Apple will come iup with a cure. THIS IS RIDICULOUS that hundreds of their customers should have to waste their time going through this ridiculous excercise. Thanks for ALL your help (ON & OFF this particular topic!)