Just bought the MX Keys for Mac and used the Unifying receiver because I read bluetooth won't work when using Filevault because the bluetooth driver isn't initialized yet. I also have a Master 2S for over a year via bluetooth connected which worked fine so far, not a single outage all the time. But since I connected both devices now with the receiver, I get lags multiple times a minute for a few seconds both with mouse and keyboard and for the keyboard every now and then also disconnects where the device 1 key (F13) starts flashing. Not what I hoped... but since bluetooth works fine I'll stick with that and set device 2 to the unifying receiver. So I can enter the filevault password on device 2 and use it normally on macOS on device 1. But I'm not sure why that's happening. I reinstalled the Mac recently and this time didn't mess with it. I still have SIP enabled, don't have Homebrew installed and only used official apps so far and didn't mess with admin privileges.