The Pixel 3 and Pixel 3 XL have not received the November 2021 security patch, a sign that Google has ceased software support for the pair. However, the company has confirmed otherwise. Project Mainline should also ensure software support beyond the Pixel 3 and Pixel 3 XL's final update.
https://www.notebookcheck.net/Google-confirms-one-more-update-for-the-Pixel-3-and-Pixel-3-XL-after-November-security-patch-miss.577225.0.html