There are different versions of the KS-604S requiring different GPIO configurations. Please refer to https://tasmota.github.io/docs/devices/Kesen-KS-604S/ for more details.
I bought a KKCool KS_604S from amazon.com on 12/17/2020. It was still tuya-convert-able;-) I don’t know about the GPIO mapping yet because it’s not installed yet. I opened the back and the all the needed connections are easily acessible. So, there should not be a problem, even if the firmware would be updated in the future.