We (large arline) don’t and never have. I assume the original safety case came out against it as Swissair/Lufthansa above, so sensible heads prevailed. The whole point of a locked door is to stop breaches of the flight deck, even by someone who knows how the locking system works - this was proven effective in the Eurowings crash. It’s also probably easier to have a “sleeper” as CC than a pilot, so the threat surface would be expanded by the two-rule.