Just a data point from experience (edit: April 2024):

Flew LHR-HKG, then two days later HKG-HKT.
At the time of our flight to Thailand we had about 5 months of validity left, CX still issued our boarding passes (even via OLCI - we got mobile passes and then printed ones at the airport) and let us on the plane. On arrival, immigration did raise eyebrows and mentioned the 5 months remaining, but let us through anyway.

Our return (out of Thailand) was on the same itinerary/PNR, if that's any help (flying out from BKK-LHR via HKG, no stopover).

When I first discovered that we had less than 6 months on our passports, we were frantic to get a 1-day premium passport, but seems like CX and other IATA airlines follow Timatic to the rule. This has worked for us as there was no mention of the 6 month validity rule on Timatic.