Google is expected to release the first Android 12L Beta sometime this month. Before that, Lenovo Tab P12 Pro users can install its Developer Preview 1. The "Lenovo P12 Pro Android 12L Developer Preview Program" is available directly from lenovo.com instead of from Google. It runs the 2021-11-01 security patch and is supposedly the "first large screen optimized Android OS with new APIs for application developers to provide a better app usage experience in landscape mode, including easier multitasking, system UI optimization, and more." (We're raising our glass for Android 3.0 Honeycomb.)
Lenovo warns that this DP1 is "intended for application developers only." They can find install instructions here. 9to5Google listed the "limitations" of this preview, and Lenovo says it only works with the Wi-Fi model (Lenovo TB-Q706F).