Flash device via Raspberry Pi GPIO header

I know there are other options - many other options. I’m asking if it is possible, and if anyone knows how to do it this way.

I just purchased a couple of Sonoff S31 outlets I’m adding to my HA setup. I haven’t used my FTDI board in a couple of years, so had to order another - It’s in that place I put it so I’d be sure I’d remember where it is. While the replacement is on the way, I realized the RPi should be able to do this pretty easily. It has 3v3 out and the GPIO pins are 3v3 (5v tolerant).

Has anyone done this using the GPIO pins on the RPi that is running HomeAssistant OS to directly flash a device like the S31? Everything I’ve tried in searching for this completely washes out the actual context of my question - responses include how to run HA on a Pi, how to flash a device from a Pi via USB, how to have HA control Pi GPIO pins for input and output like switches and sensors.

I have tried /dev/ttyS0 (UART0), which uses GPIO14 (pin 8) as Tx, GPIO15 (pin 10) as Rx, 3v3 and ground, but HA doesn’t recognize the S31 as a serial device. Yes, I did cross over Rx and Tx, and I held down the S31 button while I connected power to it.

I have lots of experience with the Linux command line, but absolutely zero with the HA command line.