I've only used Google Maps for navigation myself so can't speak to what Rivian does. But Google Maps uses Internet access to determine the speed of traffic on your route, allowing it suggest alternate routes if there's a traffic jam. (It also uploads the speed that you're traveling to Google servers, which is how they know about traffic jams to begin with: in many cities they could buy data from traffic cameras, but in stretches of rural highway where there are no cameras, Google Maps still knows when traffic has slowed down to a crawl. Guess how.) It also uses the Internet access to access reports like "There's a police car / stalled vehicle / object on road ahead". It may do other things with Internet access that I don't know about, but those are the two that I do know about.

And at least the object-on-road feature is one I'm glad they have. I once saw a truck ahead of me in my lane suddenly swerve hard onto the shoulder, which alerted me to danger. (The truck driver remained in control of the truck, thankfully). And there was a wooden pallet lying squarely in the right lane of the highway. I avoided it by moving into the left lane, then once I spotted a mile marker I pulled over and called 911 to report the traffic hazard. About ten minutes later, as I was driving on, I saw a police car on the opposite side of the highway, heading towards where I had reported the pallet on the highway. No way of knowing whether that car was the one responding to my call, but the timing suggests it was. Hopefully nobody had an accident before the pallet got cleared away. These days Google Maps would be able to alert people to the hazard before they got close, so nobody will be in the situation I was where the vehicle in front of them blocked their view of the hazard until they were quite close.

Long story short (yeah, yeah, I know: "too late"), some Internet-required features of modern navigation are ones I'm glad they have.