Android 12 developer preview has been released to public access on February 18, 2021. Developer previews are released for developer feedback on upcoming features of the new version of android OS. This goes without saying that the feature may break and not for daily use basis. Based on feedback & feature stability some of the features may not make it to the final stable release of Android 12 which can be expected by September of this year.
Developer previews are ideal times for any app developer to test their existing app for the latest changes to underlining Android OS. Surely this avoids getting bad reviews on the play store for your app if there are breaking changes in it. You can try the Android 12 developer preview on the Pixel 3 and above series. Don't worry if you don't have a Pixel phone, Android emulators always come to the rescue for the Android fragmentation issue, moreover now Android emulator has significantly improved performance which makes testing on it easier.