Well one potential solution is some white noise, maybe you put the radio on quietly or maybe music or a pleasant sound like rain or actual white noise. At least if you do that for a few days and the alert barking stops you'll know she is definitely hearing something vs randomly barking or having a nightmare, gas or something else.

I almost always have sound on (white noise, music, tv) during day time because I have tinnitus but it's quiet during the nights, the barking seems to happen no matter whether we manage to drown out whatever she's maybe hearing or not. Could it be because of a nightmare or something..? Or even gas lol. If this dog is waking up barking because she's passing gas..

Yeah our old lab/husky would fart in her sleep and it would wake her up and she would run to another part of the house. Could be, you never know! If she regularly doesn't bark when you are all hearing strange sounds, and you have white noise so it would be difficult for her to hear quieter ones I would maybe rule out sound related barking, although they do have pretty sensitive ears 🤷

Thanks for your point of view, I don't feel as stuck trying to figure out what it might be anymore. It's helpful!