[Google Pixel 4 Guides, News, & Discussion] i5lee8bit:
EASY UPDATE / SEAMLESS KEEP-ROOT UPDATE PROCESS

(using a PC - a very intuitive, effective, and relatively safe method).

** You can only follow this guide verbatim if coming

EXACTLY from build "11.0.0 (RP1A.200720.009, Sep 2020)"

. But the general idea is the same for other builds, you just need the correct files for your device.

flame-rp1a.200720.009-factory-dtbo.img: https://www.androidfilehost.com/?fid=10763459528675562111

flame-rp1a.200720.009-factory-boot.img: https://www.androidfilehost.com/?fid=10763459528675562110

September 2020 sideload OTA zip: https://dl.google.com/dl/android/aosp/flame-ota-rp1a.201005.004-9e17c7b4.zip

DO NOT BOOT BACK INTO O/S UNTIL ALL STEPS ARE COMPLETED - THIS ENSURES EVERYTHING BOOTS BACK UP WITH MAGISK / EDXPOSED ALL RUNNING PROPERLY RIGHT AWAY

1. boot into bootloader

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** I was on custom kernel, so I needed to flash BOTH the stock boot and dtbo images

2. fastboot flash boot flame-rp1a.200720.009-factory-boot.img

3. fastboot flash dtbo flame-rp1a.200720.009-factory-dtbo.img

......* these steps to restore stock recovery; dtbo.img also necessary for some kernel installations.

......* won't hurt to flash both anyway, so if you're unsure, go ahead and do both.

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4. use volume keys to change selection to boot to Recovery Mode

......- when you reach the android symbol with No Command, hold power button, tap volume up, in case you've forgotten

5. choose option "Apply update from ADB"

6. adb sideload flame-ota-rp1a.201005.004-9e17c7b4.zip

7. Once the OTA sideload is done, Reboot to bootloader (you'll also notice it's now on the other slot after OTA flashed)

8. fastboot flash boot flame-rp1a.201005.004-magisk_patched-21.0.img

9. done, start the phone

(Optional - Flash custom kernel. If you had a custom kernel, you need to re-flash it)

This is a 100% seamless update that requires no additional / re-setup of any of my Magisk or EdXposed setups. All of the factory files can be found here https://developers.google.com/android/images. boot.img and dtbo.img are in their corresponding full Factory Image zips, and the ota zip is under Full OTA Images.

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Issues after updating?

If you end up unable to boot or bootlooping afterwards, you most likely have an old Magisk module that isn't playing nice with the new build. There are 2 main things you can do:

1. Flash the new factory untouched boot image. You will of course lose root, and all modules will be disabled. However, it should at least get you able to boot back up quickly and have a working phone if you're in a bind.

2. I would recommend checking Tulsadiver's thread: https://xdaforums.com/pixel-4/how-to/magisk-modules-disabler-booting-magisk-t3991739

Instead of reverting to stock boot image, fastboot boot (NOT FLASH) Tulsadiver's boot image. This will boot your phone in Magisk Core-Only Mode, with all modules disabled but root retained. From here you can open Magisk Manager and disable suspect modules. Before rebooting, go to Magisk Manager's settings and disable Magisk Core-Only Mode. Once you disable the incompatible module, the phone should boot back up.

- See this post (or thread) for more tips / context / an example: https://xdaforums.com/showpost.php?p=82509691&postcount=16