[OnePlus 3 & 3T Cross Device Development] Johannes1098:
My current situation

- LOS 16 20190611

- OpenGapps 20190611

- Magisk 19.3

- 5.0.8 Firmware

- encrypted F2FS file storage with boot-PW

- TWRP 3.3.1

- unlocked BL

My goal

- LOS 16 20190620

- OpenGapps 20190620

- Magisk 19.3

- 9.0.3 Firmware complete - also with new Keymaster and Bootloader from 9.0.3 (I prefer to make the upgrade complete, the fix with the old keymaster and BL is not more than a temp workaround for me...)

- encrypted F2FS file storage with boot-PW

- TWRP 3.3.1

- unlocked BL

- ALL DATA AND SYSTEM PRESENT

Therefore, here are my steps how I did it:

1. Nandroid Backup with TWRP 3.3.1 (only backed up /data because /system and /boot I could reinstall with the installation zips..)

2. Backup the whole internal storage (via adb pull -a /sdcard C:\destination) - MTP protocol is too unstable

Also - of course - transfer the Nandroid Backup to your computer (as it's in the internal storage this should go in one step..)

3. Checked in developer settings that the Bootloader unlock is allowed (important - if you cannot boot to system and recovery with locked BL you have to unbrick the phone - more work for your..)

4. Closed Bootloader in fastboot with "fastboot oem lock"

5. Booted to TWRP but couldn't decrypt data (may I had to delete the boot-PW, could be the issue..? I dont't know.)

"default_password" also didn't work

6. So I clicked cancel at the TWRP decryption page.

Then "Wipe", "Advanved", checked /data and then "Change Filesystem". Then "changed" it to F2FS (it was already on F2FS of course - but I had to get rid of the corrupt data)

7. Just to be on the safe side: reboot recovery

/data was now accessible again

8. Wiped /system in TWRP

9. Copied Firmware 9.0.3, LOS, OpenGapps and Magisk to the device and installed them in the same order.

10. Booted up LOS to check Baseband version (MPSS.TH.2.0.c1.9-00102-M8996FAAAANAZM-1.197095.1.198697.1) All fine. (System wasn't encrypted at this point any more of course)

11. Opened bootloader in fastboot with "fastboot oem unlock". Now it booted to TWRP - and the data wasn't deleted. So I think at locking the BL, the problem was the decryption (or maybe only the boot-PW, I also don't know)

12. Now I encrypted the device including a new boot-PW in LOS

13. Back in TWRP, after now successfull decryption I copied all the backup data to the phone

14. Restored /data Nandroid backup

15. Booted up the "original" restored system, system could decrypt data and booted

But I could not unlock and FP wasn't recognized - this problem is already known

16. So I booted to TWRP and deleted those files with the TWRP file manager:

/data/system/locksettings.db

/data/system/users/0/fpdata/user.db

/data/system/users/0/settings_fingerprint.xml

Now after boot into LOS, I could unlock it.

17. I set a new pin for the system (could be the same as boot-PW, but doesn't has to..) and installed fingerprints

Finished: Now I have the newest LOS 16 with complete 9.0.3 Blobs, Firmware, BL and keymaster and ALL my data

At this point I just want to say: Thanks to OnePlus for this wonderful "bug"! :D

Seriously: I want thank [MENTION=5091734]dianlujitao[/MENTION] for providing TWRP and LOS for us. It's a huge advantage for "old" devices such as the OP3.

And of course also thanks to all other LOS developers and LOS experts in this forum (just to mention a few: [MENTION=1763460]Dirk[/MENTION] [MENTION=4405529]nvertigo67[/MENTION] [MENTION=9708417]Eric_Lev[/MENTION])

Hope this instructions could help anyone who also wants to update to 9.0.3 firmware..