[OnePlus 9] EtherealRemnant:
It seems lots of us have had to use the India 9 Pro MSM to recover our devices and in the process, we lose the ability to go back to OOS12 or ROMs based on that firmware because the touchscreen stops working and also trying to convert T-Mobile variants, the fastboot scripts are just bricking them. Well I found a fix for these issues. Those who just want to convert can skip the MSM Tool process and get right to the conversion process as long as they're already running OOS11.

First thing is first, you need to be on OOS11. If you have a T-Mobile variant and you have flashed it with India firmware, you have to use a modded T-Mobile MSM: https://xdaforums.com/t/global-11-2...ariant-flashing-as-well.4454357/post-87050821

If you have a T-Mobile variant that hasn't used the Indian 9 Pro MSM Tool, is on OOS12, and you're just wanting to convert, you need this tool: https://xdaforums.com/t/oneplus-9-11-2-22-2-t-mobile-msm-download-tool.4276119/

If you have a global variant or a global variant that has been flashed with Indian firmware, you can use this MSM (choose O2 for global or India for India in the Target dropdown, check Sha256, uncheck use lite firehose, it's a multi-target MSM Tool): https://mega.nz/file/ZWtGxTSb#UZ6aSOR2UTYrCao2fQNJ1IN5LSxPNBOxzel1kihnnJs

If you don't know how to use the MSM Tool, there are other guides around here, that's outside of the scope of this post.

Once you are back on OOS11, unlock the bootloader. We also need USB debugging enabled.

Now we need a tool called Fastboot Enhance. This wonderful tool allows you to directly flash OTAs from fastbootd and it doesn't have the same brick risk that flashing with fastboot scripts does.

Download it and unzip it somewhere.

Next we need the OOS11 global downgrade package (or whatever region you are wanting to switch to, global is recommended for T-Mobile variants) from here: https://xdaforums.com/t/oneplus-9-rom-ota-oxygen-os-repo-of-oxygen-os-builds.4254579/

Fire up command prompt in the folder you have your platform tools and run:

adb reboot fastboot (if you do adb reboot bootloader you will then need to type fastboot reboot fastboot to get to fastbootd)

This will take you into fastbootd. It will have a screen that has three different languages to choose from on it. Go ahead and fire up Fastboot Enhance now.

It may take a few seconds for the app to recognize the device but when you see it in the list, double-click it to get to the main screen.

View attachment 5644059

Check that it says that the device is in fastbootd. Now we just need to click Flash Payload.bin and choose the OTA we downloaded earlier (we don't even need to extract the zip, the app does that for us). If it pops up with an unrecognized partitions error, you're either not in fastbootd, you didn't MSM back to stock (you cannot do this with a custom recovery), or you grabbed an OOS12 OTA. Do not continue and check that everything is correct otherwise you will brick and have to start all over with the MSM Tool. Likewise, if it pops up an alert about cow partitions, don't continue. Go to the partitions screen and search for cow and delete them all.

Once it's done, boot the device, factory reset it in the settings (this is mandatory as Fastboot Enhance does not erase the device like a normal downgrade would do and this can cause problems), set it back up, and then do the OTA process to get back to where you want to go.