The Android Police team initially spotted that when the dark theme is applied on the Google Pixel, it looks more like a dark-grey-blue than AMOLED black. If you do prefer the potentially battery-saving pitch-black color scheme, then this might be frustrating for you.
The dark theme shade with the Android 12 Developer Preview is not a pure dark black color, says Android Police. It is you who needs to decide whether you like it or not. Some might not care, and some might get frustrated with this new update.
It is weird how the apps and app drawer has a dark theme, whereas the rest of the phone has the new grey-blue music. This quirk could mean two things, either it is evidence of the availability of further customization options. If not, it is just something that we all have to live with until the next Android update.
All we can do now is to hope for more options in the theme section. Undoubtedly, the potential dark theme change in Android 12 will infuriate a few people to some extent. The users can surely skip the Android 12 update until there are further changes made, but that would be a short-term solution.