[OnePlus 12R / OnePlus Ace 3] Advali:
First of, I know that there might be post/comments in this Oneplus 12R forum already on how other users have managed to convert their Ace 3 to 12R.

Some have managed to flash to 12R but without a working signal or WiFi. Others flashed the ColorOS OCDT and oplusstanvbk after conversion but lost their signal after an OTA.

And although one of the main OP here @Jookean already posted his method to have a fully working 12R conversion, unfortunately some users have failed their attempts for conversion leading to either bricking their devices or simply losing their bootloader so I've decided to create a separate thread detailing how I converted my Ace 3 to 12R.

Note that, same as @Jookean 's guide, this is not a perfect conversion which I will explain later. But for the most part, some of the steps have already been detailed either in these 2 threads:

Thread 1: https://xdaforums.com/t/12r-ace-3-e...tore-your-device-to-oxygenos-coloros.4654245/

Thread 2: https://xdaforums.com/t/ace-3-convert-ocdt-23801-to-23861-ace3-to-12r.4656497/

Does relocking the bootloader works after flashing? Yes

Does Mobile signal and WiFi works? Yes (somewhat for mobile network, I'll detail why in the post below)

Does OTA work without losing signal? Yes

A few things to note on my method compared to Jookean's: I didn't use the official MSM/download tool method but simply used the SM8550 Flash Tool or the new method posted in Thread 1. Its much simpler to use and I don't have to install proxifier/python etc. Basically it just works for me. And I unfortunately get an Error "Failed to flash sign from server" when using the official download tool while flashing the 12R firmware so I basically gave up at that point (even though I've already flashed the 12R OCDT). Well, If it works on your end, then great :) Either way, I'll only be using the Flash Tool just once.

Next issue on my end is that compared to Jookean's method, its only 3G that isn't working from his end. In my case, its mostly 4G/4G+/LTE/GSM that is working without disconnections (and I have to use a separate app to force it) and if I switch to 5G or 5G/4G/3G/2G (auto), sometimes it works but most of the time the radio somehow disconnects/turns off and on continuously. Maybe because I didn't flash the entire 12R firmware with my method and I've managed to left out some additional IMG files to be flashed as well causing some applications from ColorOS to still be available (but you can easily uninstall them directly without issues). So basically if you need 5G then maybe look for another guide somewhere or wait til we manage to sort this issue out. In my case 4G/4G+/LTE connection is fast enough for my daily use. Again, 5G does work sometimes (forcing 5G only) but somehow it tends to disconnect/turn off and on in my case consistently.

So having read that, here are my steps:

1. Flash your Ace 3 back to 14.0.0.305CN01 Firmware using the ff firmware below and the new method from Thread 1. Just follow the steps and don't forget to overwrite the prog_firehose_ddr.elf under <Firmwarefolder>/IMAGES (from the downloaded firmware file below once you've extracted it:) All the files needed are already in that thread.

PJE110domestic_11_14.0.0.305CN01_2023122613020116.zip

drive.google.com

2. Download my CPH2585 / 12R firmware flasher - ONEPLUS_ACE3_PJE110_TO_CPH2585.rar (contains the firmware files as well):

ONEPLUS_ACE3_PJE110_TO_CPH2585

MediaFire is a simple to use free service that lets you put all your photos, documents, music, and video in a single place so you can access them anywhere and share them everywhere.

www.mediafire.com

3. Unlock your bootloader and Root your device. You can use the guide from @amirhidd3n from here: https://xdaforums.com/t/how-to-root-oneplus-12r-a-complete-guide.4663162/

You can skip the part where you have to download a separate firmware with payload.bin. Basically you can just use or extract the init_boot.img file from the downloaded ColorOS firmware from step 1 (it should be under <Firmwarefolder>/IMAGES). Use that file and patch it in magisk then flash the modified init_boot using the steps from the link above.

4. Once you're rooted and have magisk installed, you can now backup your OCDT file by opening a terminal/command prompt where your ADB executable is located and running:

The OCDT.img file will be copied to the root of your storage so just back it up or copy it to your computer.

5. Still inside the adb shell, copy the bdwlan.elf or wifi driver using the ff command:

to check if the file has been copied successfully you can use the command:

and you should be able to see the bdwlan.b0i in that directory. This directory is persistent so even if we EDL back/format/relock bootloader, this file will not be deleted.

6. Convert the OCDT.img file to global using the guide in Thread 2 or simply go to this link https://vnncv.io/ocdt/23861.html and upload your original OCDT.img and then download/generate your global OCDT.img file. Initially it will be named as ocdt_23861.img but you can rename it later.

7. Now open another ADB instance via a terminal/command prompt and enter:

From here, you'll need to flash the global OCDT file you've downloaded (ocdt_23861.img) and once you're in the bootloader type in:

8. Once successful, navigate to where you've extracted the ONEPLUS_ACE3_PJE110_TO_CPH2585.rar file and navigate to the directory containing Flash_12R.bat

You can run the Flash_12R.bat file while in bootloader mode as it will automatically reset your phone to fastbootd mode and once you're in fastbootd mode, just follow the direction on the command prompt/terminal when it says to press any key/button.

Note that there are 2 img files I forgot to include which is my_company.img and my_preload.img since I accidentally deleted the firmware so this will probably cause for some chinese apps to be available after the flash, just simply delete them after booting. I also tried flashing the missing files from the 2611 firmware and it works on my end but just to be safe, I didn't include them to the current rar file assuming it may cause some issues on your end. Either way, again, just uninstall any remaining chinese apps in there (or you could include the my_company.img and my_preload.img from the 2585 firmware)

9. Once you've successfully booted to OOS, you can now relock the bootloader. At this point, you'll have both mobile signal and WiFi (although there might be some issues with the mobile signal which continuously turns on and off but we'll fix that later. If there isn't any issue on your end then great :)

Enable developer options again, open an ADB terminal and type in:

Once you're in the bootloader, lock the bootloader by typing:

Use the volume button to navigate and power button to confirm the selection for locking the bootloader. It will factory reset the phone again.

10. If 5G isn't working on your end or the mobile signal turns on and off continuously, switch the connection to 4G/3G/2G Auto and download the app 5G 4G Force LTE Mode in google play and force the connection to use LTE. In my case (LTE/TDSCDMA) is the one that works great without my mobile network turning off and on.

Assuming the 4G/3G/2G option isn't available from your end, then update to the latest software update 14.0.0.500

11. When you first try the OTA the update size is around 1.39GB. This will initially fail, don't worry about it, once it retries, it should download the 5GB+ update instead and you'll be able to update to the latest version.

12. Assuming you have issues with your mobile network/data, you can try a different network combinations using the 5G 4G Force LTE Mode app.

Again if 5G is important from your end then you could try the other guides or have a crack on probably fixing the issue (or you could try and test if 5G will work flawlessly on your end, I'm really not sure since I've only tested my phone for this). I'll try to have a video created if I'm not busy but I'm planning so once I figure out the issue mobile network disconnecting issue and I'll try to update the guide with images later if needed.