I just had an Action 2 delivered to me and the box had a manufacturing date of 11/2021. While flipping through the owner’s manual, a blurb on battery storage mentions that a battery should not go unused for more than four months otherwise battery life will be reduced.

As this unit was boxed approximately 7 months ago at the factory, does my new unit have batteries that already have their health impacted?

Thanks!

Probably not as they are put into a hibernation state before they leave the factory and stay that way until you charge them.  I've had batteries come in that were 8 months old and have had no issues with them whatsoever.