I've been studying English for several years now and recently I've started to follow a Facebook group in which there are mostly people from the US. Beside the fact that they use so many acronyms (some of them are quite difficult for me to understand, as we don't use them so much in Italian!),I've found some very curious grammar forms that I've never seen before and even Google couldn't help me. A woman wrote "So we weren't gone on holiday." It is correct?
The word "gone" can be used as a verb (go, went, gone), adjective or preposition (https://www.merriam-webster.com/dictionary/gone).
Is/are/was/were/have-has been gone
All of these variations would be grammatical so long as the word "gone" is used as an adjective.
We were gone by the time he arrived (We were no longer present at the location in question).
'Gone on holiday' is an idiomatic phrase, and should be considered as a whole rather than as part of the verb 'to go'.
Luckily we were gone on holiday when the house burned down, so no one was hurt.
Here "gone on holiday" is a state or condition of "being away on holiday".
It is quite different from "we were going on holiday".
It's colloquial. A bit more unusual as a negative, I think, but on an informal FB page people can speak how they like. What your FB poster means is "We weren't in the state of being on holiday", ie "We weren't away".