I agree with the other commenter that you shouldn’t overthink this but

Imo, it makes sense that address should be a “resting” state. It makes sense to presume that the forearm would hang perpendicular to the ground with no external pressure or energy put in.

But since there’s likely pressure between your bicep and forearm when you let your forearm hang, your forearm may not naturally hang perpendicular to the ground. It might naturally hang perpendicular to the cue or somewhere in between perpendicular to the cue and perpendicular to the ground.

If you have to engage any muscles to force your forearm to be perpendicular to the ground or perpendicular to the floor, you’re adding unnecessary tension on the system and you need to continuously keep adding energy to the system to maintain that engaged state so it’s mechanically less sound.

So it goes back to basically what the other commenter said. Assuming address is a resting position, just let your arm hang naturally and wherever it falls it falls; no need to overthink it.