Almost nine years have passed since Asus marketed the Nexus 7 version 2013, a device born with Android 4.3 Jelly Bean that has continued to receive updates up to Android 6.0.1 Marshmallow; his time seemed over but, with Android never say never, in fact, the developer community, thanks above all to the XDA forum member follows, has given new life to the tablet in question thanks to an unofficial version of LineageOS 19.1 with Android 12L.
Let me be clear, the procedure adopted by the developer to achieve the result was not very simple and the ROM is still in the beta test phase, so it is possible that there are also numerous bugs and various problems, but basically, on such an outdated device it is more what else than an exercise in style, do it because it can be done.
The ROM is available both for the WiFi version (codename flo) and for the variant with SIM (codename deb), among the hassles you may encounter during installation is the need to partition the device memory ( operation possible either via TWRP or manually via shell) in order to install a gapp package; furthermore, as often happens when projects of this type are in their infancy, SELinux is set to permissive, so not the best of life when it comes to security, especially for the average user. Nonetheless, the flash of the ROM will bring to your old and dear Nexus 7 2013 not only all the latest security patches but also a whole series of new privacy features, as well as Android 12L features.
If you are interested in trying it, just follow this link and read carefully what is reported to be able to install Android 12L on your Nexus 7 2013.