Apple CarPlay in 2021 BMW suddenly not working?

Try the following if you are exhausted from forgetting devices and reconnecting etc on your iDrive and iPhone. Try this, it worked perfectly: How do I reset my BMW Connected Drive?

To reset your BMW you need to press the volume button and hold it for about 20-25 seconds while in standby (ignition on, engine not running). Then press the volume button again and you should be all set.