maybe it's time to post a success story here...
and i take it back. creality DID post a how-to for BL Touch on Ender-6:
I can confirm that the firmware 18.104.22.168 and BL touch 3.1 do play nice together.
i used one that was labelled for ender-3 v2.
bought another picoblade connector (pre-wired), cut the big connector off the bl touch cable, wired the new one up colour-for-colour (ok, green was supposed to be white). otherwise it was plug and play, following the video exactly step by step.
i'm pretty sure using a fresh-formatted empty sd card is a step missed by a lot of people who later have problems. or not having the bl touch connected during flashing (or "brushing" as creality calls it) or during startup. and dont forget to disonnect the Z end-stop. if testing before mounting the unit, make sure it's vertical so the pin can drop freely.
also, before i soldered on the new cable end, i tested with some alligator clips. the ender did NOT like that at all: all the stepper motors growled like an angry wolf pack whenever BL was plugged in. pretty scary, but luckily the final cable solder job stopped this. I assume it was interference with PWM.
only thing left to solve is how to store the bed mesh and z offset, so it doesn't have to measure after powering off.