It took several years for Google to allow Android Auto head units to run third-party navigation apps instead of its own Maps service. As expected, Waze was the first on board, then more followed suit, including TomTom NaviGO. But all of those are made for typical route-following drivers. What if you want to take your 4x4 on an off-road adventure? You'd need a specialized app for that, like Gaia, and now it's just landed on Auto.
Gaia is a popular off-road mapping service (though it offers tracks for hikers, boat riders, rock climbers, bikers, and snow sports enthusiasts too). Its latest beta v2021.6 adds Android Auto compatibility, so users can safely navigate their saved routes on the large head unit in their car instead of repeatedly checking their phone. Attention is crucial in these wilder environments, and it's definitely better to keep your eyes peeled on the "road."
A help article on Gaia's site explains everything you need to know about the app on Android Auto, but the gist is that you need to join the official Play Store beta and wait for the app to update on your phone, then sign in, and make sure you've created drivable routes (i.e. in driving mode) on the app or site.
When you connect to the Auto head unit, Gaia will be available in the launcher and will show your current location as well as the six routes that are the closest to you. You can search for other routes too or select them from the app on your phone. Start one and you'll get your directions and trajectory details. The app supports light and dark modes, has Assistant integration, and various customizable map overlays. If you'd like to give it a try, start by joining the beta.