After watching all the videos I was having similar issues. I ran the "hello world" screen demo through the Arduino IDE then I unplugged the machine and was stuck with the "hello world" demo. I then was unable to get the cardputer in "download mode" after trying to use the m5 burner several times. I'm on a m1 mac btw. Using a usb c <-> usb c cable. It was showing up as tty.usbmodem1101 but only when the device was turned on.
I was trying to recreate one of the videos by trying a bunch of different orders of plugging in the wire, combinations of "on and off", holding the "go" and holding the "reset" buttons on top the device.
I found that holding "go" would prevent auto-on when plugged in. When I did that and the pressed "reset" I think that did the trick.
So for me it was "hold go", plug in, spam "reset", try and burn...