It's highly unlikely you'll get a definitive answer to this, until all of the shows that were in production before and immediately after Infinity War was released have aired. Marvel has never said how much information is shared between Marvel Studios and Marvel Television, and I can't think of a reason they ever would do so. So, the only chance of really getting an answer is if someone on the inside decides to talk about it. Of course, if half the people in Cloak & Dagger are suddenly gone by the end of its first season, then its writers would have obviously had advance knowledge of what happened in IW, since C&D finished filming last Fall.
I will say that my guess is that the showrunners probably weren't given advanced notice. Since Marvel Studios was separated from Marvel Entertainment (the parent of Marvel Television), the TV shows haven't seemed to have much interest in connecting with the movies. There hasn't been more than vague references to them. The heads of the newer shows like Cloak & Dagger and New Warriors have given interviews that make it sound like they just don't want to think about the broader universe.
I imagine that Marvel Television would like to completely ignore the events of Infinity War. As you said, it seems hard to ignore half the population disappearing, though, so they might be forced to. But even if so, they'll probably wait to do so. The timelines of their current shows are either noticeably in the past (e.g., the Netflix shows), or are ambiguous enough that they could be taking place before IW. And, if they can wait until after Avengers 4 is released, since that movie will almost definitely undo the finger snap, the shows might be able to get away with not referencing it.
Assuming that's their mindset, there wouldn't be a need for them to know about the events of IW in advance. And without a need, I'm sure Marvel Studios wouldn't have given out any details.