You REALLY need to get back the ADD NEW DEVICE option. I had to install the old Logi Options version, activate the Advanced Unifying App/Advanced Options, unpair the MX3 mouse from the old dongle (which I luckily kept around and was able to turn back in) and only then I was able to pair both new keyboard and the mouse to the new dongle (when I unpaired the mouse from the old one). IMPOSSIBLE OTHERWISE, NO BUTTON COMBO WORKS, EVEN IF YOU REMOVE THE OLD DONGLE! YOU HAVE TO UNPAIR IT FIRST! (See the attached image). By the way, is it possible to download the Advanced Unifying App separately ?! If so - where ?