Android 10 から Android 11 にするために、これを試していきます。
Official StatiXOS 4.1 Release (Android 11) | XDA Developers Forums
https://forum.xda-developers.com/t/official-statixos-4-1-release-android-11.4211651/
安定性は先述のより不安があるけどこちらが焼けたのでこれで運用しよう。
[ROM][11.0][UNOFFICIAL][MATA] Evolution-X 5.4 [2021.02.12] | XDA Developers Forums
https://forum.xda-developers.com/t/rom-11-0-unofficial-mata-evolution-x-5-4-2021-02-12.4233237/
Mobile Network can't be used in my phone. This issue is not reported and maybe only my situation. Take a look another ROM.
Btw, I notice that StatiXOS which I downloaded is not for Essential Phone(mata). I need to check it carefully.
New StatiXOS OFFICIAL 4.2 build for Essential PH-1 | XDA Developers Forums
https://forum.xda-developers.com/t/new-statixos-official-4-2-build-for-essential-ph-1.4242099/
Android 11 のカスタム ROM だとモバイルネットワークの認識がおかしくなるな。
@Chrisleon27 I set it small. 
Reported issue that crashing of Chromium Browser of course happened on my devise, but other functions seemed Okay. Just use Firefox.