Google promised over a year ago that the wireless version of Android Auto would work out-of-the-box on any Android 9.0+ phone, but that hasn't quite panned out. The only devices that have been able to use it are Google's own Pixel devices (plus the Nexus 5X and 6P), but that finally appears to be changing.
A Google support document was just updated to state that several Samsung Galaxy phones are now compatible with Android Auto Wireless, including the Galaxy S8/S8+, S9/S9+, and S10/S10+. The Galaxy Note 8, Note 9, and Note 10 are also compatible. In all cases, the phone has to be running Android 9 Pie or newer with (at least) version 4.7 of the Android Auto app.
Of course, you'll still need an Auto head unit (or a car) that supports the wireless mode, which can be fairly expensive. JVC just released two more options — the $500 KW-M855BW and the $600 KW-V950BW.
The Android Auto site has been updated to list more wireless-compatible head units. Here are the new models from Kenwood:
The Pioneer page also mentions some new non-wireless head units:
Galaxy S20 and Z Flip
Google now says that Android Auto wireless is supported on "Other Samsung devices (incl. Galaxy S20 and Galaxy Z Flip)," provided they run Android 10 or higher. It's not clear if that means all Samsung devices on the latest Android version will be compatible or just some select models, but at least we know the newest S20 and Z Flip are supported.
- Google Support