How to go back to stock

Just unzip and open flash.bat file and connect phone in Bootloader mode.

MAKE SURE YOU HAVE DONE fastboot flashing unlock_critical before flashing

MD5:00599a30b332dfbd95d7d568b1cb30b1

https://drive.google.com/file/d/1_aPe245m9QrFxNChPiu3Gu5541A2jNwH/view?usp=sharing

Once you install this, go to system updater and local install this: https://oxygenos.oneplus.net/7333_sign_CPH2487_11_A_OTA_0420_all_ydcLoP_00011011.zip

After this you're done!