I can't seem to find any site that has the funky Android 12 beta wallpapers. I don't mean the ones that come with the beta and in the Pixel Wallpapers default app, I mean the ones in the pictures in these websites;
https://9to5google.com/2021/08/11/android-12-beta-4/
https://9to5google.com/2021/06/09/android-12-beta-2-new-features/
https://9to5google.com/2021/08/11/android-12-beta-4/
https://9to5google.com/2021/06/09/android-12-beta-2-new-features/
