I searched the posting etiquette and guidelines about matters of cross-posting but cannot find any mention of it. There is a rule about double or multi-posting, which is considered abuse and posts getting locked.
There's an old discussion regarding cross-postings from 7 years ago:
Probably a lot has changed since, but I still concur with the judgement of former moderator Rukbat and other moderators. Where do we stand today? Is it an oversight, or why is cross-posting not worth to be mentioned in the forum etiquette or posting guidelines?