Terence McKenna has some interesting (and far out) thoughts on the “communication without being detected” concept.
He would use communications that were disguised as “background noise” of space, that could not be detected unless you knew the “code”.
Yeah, seen that concept. It does look like for our species the real life answer may be quantum communications, where altering the spin of one atom that was paired with a second alters the spin of the second at any distance with no discernable radiation or intermediary transmission. We know it happens, so it’s now an engineering issue.
Even without that, it’s notable that we’re reducing powerful broadcasts from the surface as we change to viewing content from the internet or cable networks instead of broadcast networks. We may not be a giant radio beacon in space for too many more decades and it’s plausible that other species would go the same way.