The Car Key function was announced by Apple back in July 2020. It allows you to unlock the car using a smartphone. Digital keys are stored in the Wallet application. Currently, Car Key only supports select BMW, Kia, and Genesis models. However, there is hope that the situation will improve in the near future.
Apple, in particular, released a special application Car Key Tests, which is available at direct link in the App Store. It allows developers to test the integration of digital car keys with the Car Key function. Only Made for iPhone (MFi) licensees can use the application.
It can be assumed that Apple previously provided this application to partners privately. Now the app is easier to download, so perhaps more companies are testing the integration of digital keys with Car Key.