What do EBTs say about Astral Travelling?

dhatu is not about elemental and external particles but instead basic aspects or datum of dependently originated experience of suffering.

"Thus, monks, the Tathagata, when seeing what is to be seen, doesn’t construe an [object as] seen. He doesn’t construe an unseen. He doesn’t construe an [object] to-be-seen. He doesn’t construe a seer. AN4.24 AN 4.24: Kāḷaka (English) - Catukka Nipāta - SuttaCentral

Just as we do not project anything going into Nibbana, coming out of Nibbana etc, its not correct to assume anything about seeing- that it arises due to an ontological reality out there as been dealt in the Kacchayanagotta sutta SN12.15. That it is datum or experience or whatever is better not elaborated.