I only spotted this recently and I've been trawling the entire changelog without finding a mention.
At what version was 20/40MHz-XX / 20/40/80-XXXX introduced ?
It was added to the manual on 27.04.2018 and the question was asked as part of another thread in March, but never answered. So it has to be assumed, that it must have come in with version 6.42rc or some the likes.
Any definitive answer on this ?