I figured I'd centralize the instructions in a Quick Reference thread, that includes all needed file links, and an easy to follow step by step.
Please feel free to make any suggestions to simplify or make this more accurate.
UPDATE FROM 9x TO LATEST 9x FACTORY IMAGE:
* Unlocked bootloader. (*performing critical_unlock only required with bootloader versions PRIOR to TMZ20a) read it here.
* Latest SDK Platform Tools found here.
* USB 2.0 & 3.0 cables available (trust me)
* Remove screen lock security before starting
* Remove all substratum overlays
Removal of magisk modules not necessary, (they are in full operation after I flashed the zip in twrp).
TWRP 3.2.3-1 is decrypting just fine with fingerprint + pin!
Updating to the latest security patch via fastboot is pretty much back to the easy ol' days like it was on 8.1. Badger50's method is as follows.
Download and extract the latest Taimen factory image (place in Platform Tools folder)
Fastboot the latest factory image with the -w removed (in the flash-all.bat file) to both slots, and let it boot up each time. Or use the Dueces script if you prefer. (I let the factory image choose which slot to install to, I have never, one time, manually selected either slot, and it hasn't bitten me yet )
Fastboot into twrp 3.2.3-1.IMG
Flash the twrp installer 3.2.3-1.ZIP,
Flash Cust Kernel (I use Flash -not supported after 3.19 Nov 2018 or Sultan Kernel or Elemental X (EX) kernel)
Let the system boot up to verify.
Reboot back into twrp and flash latest magisk
Reboot to system
UPGRADE FROM 8x to 9x:
*Unlocked bootloader and Critical_unlock* completed. (*critical_unlock required with bootloader versions PRIOR to TMZ20a) read it here.
*Latest SDK PlatformTools found here
*USB 2.0 & 3.0 cables available (trust me)
These files on your sdcard:
* Latest TWRP.ZIP
* Latest Flash kernel
* Magisk uninstaller In the event you need to manually uninstall and reinstall MM
* Latest Magisk.zip
* Latest Magisk Manager APK
These files in your Platform Tools Folder:
* Latest 9x factory image
* Latest TWRP.IMG
1. Make backup, move to PC (because you never know)
2. Disable all security; patterns, pins, etc.
3. In Developer Options, make sure USB DEBUGGING is on
4. Connect device to PC, verify fastboot is working type; fastboot devices (should see your device's serial number)
5. Fastboot 9.0 factory image (To KEEP internal storage intact, edit and remove -w in "flash-all.bat" file and SAVE, to wipe entire device, leave flash-all unedited)
6. Type: fastboot boot <twrpxxx.img name> to boot into Latest TWRP.IMG
7. Once in TWRP, install Latest TWRP.ZIP from sdcard
8. Reboot back into Recovery, and install the magisk uninstaller in twrp, (if you get stuck at the G screen, retry running the unitstaller in TWRP a few times in a row, this HAS worked for several users)
9. Reboot back into Recovery and install Flash kernel (latest-not supported after 3.19) or SULTANXDA kernel
10. Reboot back into Recovery
11. Reboot into System, allow OS to settle for a few minutes
12. Install Latest Magisk Manager APK (install the apk like any other app, NOT from within the Magisk Manager app)
13. Reboot into Recovery
14. Install Latest Magisk.zip [If latest Magisk does NOT work try using the 1674 version],
15. Reboot back into Recovery
16. Reboot into System
If you get stuck at the G screen, or bootloop into TWRP, try these steps:
-Perform a hard reboot (long press the power button) or
-Get back to TWRP (whether by booting into it from fastboot, or rebooting into bootloader -long press power & vol down- then boot into recovery) and reinstall the Magisk Uninstaller in TWRP a few times.
- If you are bootlooping into TWRP with Magisk installed, READ THIS!
- Safety Net message in Magisk "The Response Is Invalid" is a known issue[/URL] ... Be patient
Make sure you have all the correct and/or latest versions of SDK Tools, factory image, TWRP.img and TWRP.zip, and Magisk
Note: as a matter of superstition, I reboot back into recovery each time after installing TWRP, cust kernel, and magisk, prior to booting into system. It is NOT required, but it works
Again, HUGE thanks to @Badger50 for reporting BOTH of these working processes!