You can download the Android 11 preview if you unlock your bootloader, but I wouldn't bother until Google puts out the last Android 11 Preview because you'd just end up riddling you Ph-1 with bugs. But if your Essential Ph-1 is not your daily driver/main phone, have fun, load Android 11 Preview...
https://www.androidauthority.com/?p=1086443
https://www.androidauthority.com/?p=1086443
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