Have you had any connectivity or lag issues with the MX Keys keyboard or MX Master 3 mouse?
At the moment I have the keyboard and mouse connected to my iMac Pro, in the OS, I don't have an issue.
Where I do is on the rare occasion I need to reboot. Then neither device is recognized at the login screen.
So I have the keyboard that came with the mac in a drawer at my desk and once I log in to the system both devices are perfect.
I am running straight bluetooth and I think I accidentally tossed the Logitech dongle so I am not sure if running the devices off of the dongle would fix this issue.
I have not put much effort into looking for a fix because I only reboot once a month maybe, so it is never an issue until that point, I login and pretty much forget about it.
I have read that FileVault causes these types of issues with 3rd party wireless devices but I just haven't put the time in to troubleshoot if that is the case.
Other than that, I love both pieces, My wife bought the same setup for her home desktop and work and that's been the only 3rd party mouse and keyboard she's purchased since about 2009.
Her's doesn't show a problem at login so there may be something to FileVault causing issues.
More to come I suppose.