This is a super cool bit of reverse engineering. Another interesting way to go about it would just be to examine the pinout and reflash with ESPhome. I’m betting the ESP32 ultimately only twiddles some GPIOs with maybe a bit of PWM, that was how the air purifier I re-brained with an ESP8266 way back worked.

Is the brand of air purifier mentioned anywhere? I would be interested in getting ahold of one that is already run on an ESP32.