Hello @roadfox in case you are still looking for a suitable NB-IoT SIM card. I recently got one from Miotiq which works fine for me. See here for more detail. Thanks Felix

was able to get this resolved be removing/re-installing the drivers a bunch of times. Appreciate the assist!

I am a little ashamed, it was not a driver problem. In M5burner I didn't give the information about the wifi which prevented me to burn my M5Stick. It's confusing, the error message is about a port problem. Thank you all for your answers

I also encountered the same problem when using M5 core 2. My macOS system version is 10.14.6

try the following: set the stick to power OFF plug in USB (it will automatically power ON) look in M5Burner (or in your computers device manager) if the serial port appears. If not there is a driver issue on your computer or your USB cable might have broken wires (once happened to me) if the port appears burn the factory test or UiFlow I suppose there no need to put the stick in any special mode to burn the firmware. the internal USB chip will do that for you while the programm downloads. Once the UiFlow Firmware is running you have to set the mode for wifi or usb if not already done while burning firmware.