Ok, that title takes some unpacking: A Sonoff is a microcontroller that connects to Wifi and can switch some other electrical device on and off, pictured on the right. It is basically a remote switch that can be used for all kinds of purposes, from a manually triggered remote to some fancy home automation. To flash in this context means putting a new operating system (firmware) onto the microcontroller and Tasmota is the open-source firmware that everyone seems to love and recommend.
I have had two of these switches for quite a while, but never got around to converting them to Tasmota. Earlier today I finally did, following this guide for using a RaspberryPi. The Sonoff provides an old-school serial port and wants 3.3V power internally. The only thing I had available that can do both was my Pi Zero (left in picture), and I am happy to say that it worked without much fiddling around. The most tricky part was to physically hold the Sonoff button and cables in place while turning on the Pi, then waiting for it to start up to trigger the software transfer whithout losing the connection on the cables.
Not I have to decide what to do with the switches. Probably I will go back to installing Home Assistant for central control. I have tried several years ago but I expect it to have improved much since.