If you haven't already found it, this thread
has links to the instructions to upgrade to Android Auto. It uses Mazda's firmware upgrade, so you'll have a Mazda Logo on-screen when the car starts and a red UI instead of a blue UI, but the car is a Mazda in all but name anyway. The build has been very stable for me except when I do something like plug in the phone in the middle of the boot procedure (plug it in before starting the car or wait for the home screen and there is no problem). Last time I stopped at the Toyota dealer (January 2021) they still said there wasn't a way to put Android Auto in the car.