They are supposed to draw out moisture from the bathroom so if it was vented to your attic it would just make the attic damp.

Think soggy pink fiberglas insulation between the rafters, not good, mold will love it.

You can connect it in the attic with flexible tubing to an exterior wall, through the roof, out out under the sofit. It has to go outside, just like clothes dryers and for the same reason.

The purpose is to get the moisture out of the structure, not just the bathroom. In fact, dumping it in what might be a cold attic could be worse than just leaving it in the bathroom.

If you get it to the attic, you are mostly there. Find a reasonably priced guy who does roof work to remove a few shingles, cut a round hole and install a vent on the roof and flash around it, and all you'll need to do is connect to the roof vent to the bathroom exhaust motor unit ...never vent moist things like dryers to crawl spaces or bathrooms to attics.

You can also vent a bathroom to an exterior wall. It requires no ducting and if your bath has such a wall, it's the shortest, hence the most efficient. Think about the easiest to wire method also, and which way looks better on the exterior of the house.

Licensed electrician said if it's a half bath - meaning no shower, then the vent is just for moving out air/odor. In that scenario venting to a crawl space is fine.

If it's a vent in a bathroom with shower, then, yes - vent moisture to outdoors.

I imagine the project's done by now. Just thought I'd mention...

You have to vent it to the outdoors.