Power off and unplug USB. Hold G0 (upper-right), then plug USB while still holding.
Press and hold the BOOT button before powering on or plugging in USB to enable flashing mode.
Power on and press the RESET button for 3 seconds or until the LED blinks green.
Long press the POWER button until the LED blinks.
Hold the encoder center button, then press RESET.
(CC1101 version: the button is next to the ESP32-S3.)
Make sure to plug USB to the COM programming port, hold the BOOT button and power on.
Press and hold the BOOT button before powering on or plugging in USB to enable flashing mode.
If flashing fails, run:sudo setfacl -m u:$USER:rw /dev/ttyACM0
This grants access to the serial port.