... would you be so kind as to elaborate on how I use a serial log to check the status of the S20?
A serial terminal program and your FTDI adapter is needed for serial port debugging. I use PuTTY, but feel free to use your favorite terminal program. Serial port = 115.2K baud, 8 bit, 1 stop, No parity.
ESPeasy's serial log messages are disabled by default. But you should be able to see the kernel boot messages. They will allow you to confirm the board is successfully booting.
BTW, I see that you're using an Arduino UNO to power the S20. The Arduino board is typically 5V, whereas the ESPEasy requires 3.3V. The FTDI "Friend" board will also need to be configured for 3.3V operation. Running a ESP8266 on 5V can stress it and may harm the Flash memory chip.
Lastly, the R120 bin release is ancient (stone age era, before PUYA support). I highly recommended Flashing the latest Mega release instead.
https://github.com/letscontrolit/ESPEasy/releases
For example: ESP_Easy_mega-20200426_normal_ESP8266_1M.bin provided in the mega-20200426 release.
If the S20 still refuses to boot then visually inspect its ESP chip and report if it is the ESP8266 or ESP8285.
- Thomas