Same here. Cannot for the life of me figure it out. Magic trackpad is no more than 2 feet from the mbp 16, just how my 2017 mbp 15 used to be, but it can never have a stable bluetooth connection. I've used 3 trackpads with it, reset SMC, ran diagnostics, deleted and paired again, and made sure no other devices were connected as well as turn off wifi completely with no luck. I've also moved the computer, tilted it, repositioned it, brought it closer. It's absolutely unpredictable and makes no sense. The trackpad will work just fine a good distance away but at 2 feet away on the table it'll randomly get bad signal and just stop responding or become way too jittery.
I have ALSO had multiple issues with external monitor. Again, same setup my 2017 15" was on with no issues. I've swapped dongles and docking stations with no absolute fix. I've had the computer restart with a "fatal error" or something along those lines, I've had it come back and only be able to display 30hz until i disconnect and reconnect, and i've had it stop working with a display adapter until I restart it. This has happened with a few OWC adapters and docks. I only have one large 4k monitor now, didn't get to check how it worked with my old 3 monitor setup.