Not a beginner, but have had these similar issues many years ago with my first Monome 40h, rarely with my old walnut non-varibright, and now with my 2018 grid. All my usual fixes aren’t working and I suspect I’m another victim of the fickle Apple audio driver policies.
My grid appears under devices:
But does not appear in Max 8 under monome grid-test, @neauoire’s fantastic Linn or Rack devices, OR in my old reliable Mark Eats Sequencer app that usually has the best track record of connectivity.
Running the following command:
Yields:
no matches found: /dev/tty.usb*
I’ve deleted FTDIUSBSerialDriver.kext (which is the old fix that usually works), I’ve reinstalled SerialOSC through the monome setup docs and nothing.
SO… help? 
For what it’s worth, I was initially attempting to use the grid on the Trilogy VCV rack modules and no dice, but the grid DOES work on my Norns.
MacOS Mojave 10.14.6