Some observations on One UI 4 based on
Android 12 from my side-
1. Green indicator is displayed in right corner if camera or mic is access by some app. On expanding notification, respective mic/camera symbol is seen.
2. Calendar Widget UI is slightly changed, looks more colourful.
3. Weather App UI colour changes based on weather conditions, also has 1 Widget which changes matching colour.
4. AOD has new option to display for new notification.
5. New animation of green colour circle is displayed when charging is started.
6. New animation when phone lock/unlock.
7. New stretching effect during scrooling at end of page in system UI, like settings page.
8. Lock screen notification size is small and sleek.
8. Colour Palette: Able to change notification shade and system icons/button from Wallpaper colours.
Under the hood changes are not visible or not noticeable to me.
Security Patch is Dec 2021.
Dynamic Screen Refresh which can automatically change screen refresh rate from 10 Hz to 120 Hz is missing.
Overall I can say 90% phone experience is same as One UI 3/Android 11, including my
WhatsApp notification bug 😀
Edit:
Notify Update
This link has more detailed change log for One UI 4.