I have come across multiple sources that starting in late 2021, Android Advertising ID will not be available (it will be String of zeros) on Android 12 devices when users will be opt-out of Ads personalization. One of the good sources is: https://www.xda-developers.com/google-play-services-delete-ad-id-opt-out-personalization/
To ensure the proactive handling of my app monetization for the Android 12 devices, I just verified on Pixel 4 device (running Android 12 OS) and I am able to get the Android Advertising ID after opt-out of Ads personalization. And that even without doing any extra step to target API 31 (Android 12) such as without adding any extra permission of AD_ID. Is there any clear timeline, by when it will be an effect at least for Android 12 devices? This will help us to plan the deployment in advance.