Google has started rolling out Android 12 to existing Pixel smartphones. Every Pixel smartphone from the Pixel 3 series onwards is eligible for Google's latest OS update, including the new Pixel 5a (5G). Android 12 is available as an OTA or through Google's Android Flash Tool.
https://www.notebookcheck.net/Existing-Pixel-smartphones-receive-a-taste-of-the-Pixel-6-and-Pixel-6-Pro-with-Android-12-rollout.574026.0.html