[Android Q&A, Help & Troubleshooting] Sponge2883:
Hi! Yes, of course.

Prelude:​

The device must be charged (preferably 100%)

You need to remove all locks (PIN code, face and fingerprint unlock, and so on)

You need to log out of your Google account

You need to remove all SIM cards

You need to get developer permission (click on the version number 10 times)

The rollback process:​

Download the app for local update (android 14) - click (google drive)

Download the firmware for rollback (hereinafter - ROLLBACK) and move the firmware file (zip) to the root folder of the device

Download your current firmware (if you don't know where to download it, write the full version of your current firmware, and i help u) and move it to the root folder of the device as well

Turn off wifi and any internet connection (airplane mode will not work)

Clear the cache of the application for local updates

Open the application for local updates, click on the "Gear" icon at the top right, select "Local update" and select the CURRENT firmware file. (DO NOT CLICK "INSTALL"!)

In the second window (in split window mode), open any file manager, move the CURRENT firmware file somewhere else (I moved it to the DOWNLOADS folder), copy the name, go to the ROLLBACK firmware and change the file name to the name just copied from the CURRENT firmware. (For example, the current firmware was called "2.zip ", and the ROLLBACK was called "1.zip ". Now the ROLLBACK should be called "2.zip ".

Return to the firmware update window and click "Extract" or "Install".

Wait for the process to complete. The device should reboot at the end (or suggest that you restart it - agree).

After the system restarts, get developer permission again.

Copy the ROLLBACK firmware to the root of the device

Go to device updates (without internet), click the 3 dots at the top right and select local installation

Install the ROLLBACK firmware a second time and restart the device again

Congratulations! Now you have COLOR OS 13!

The switch process:​

Repeat all the steps from the "Prelude"

Download the application for local updates (now for Android 13). Click (google drive)

Edit the files in the archives of each firmware "payload_properties.txt ": oplus_update_engine_verify_disable=0 fix to oplus_update_engine_verify_disable=1 and after "Metadata size" add POWERWASH=1 (if this line is not there).

Download the firmware you want to replace to your device (hereinafter referred to as the NEW one)

Download your current firmware to your device (hereinafter referred to as the CURRENT one)

Completely turn off the Internet, wifi (airplane mode will not work)

Open the application for local updates, click on the "Gear" icon at the top right, select "Local update" and select the CURRENT firmware file. (DO NOT CLICK "INSTALL"!)

In the second window (in split window mode), open any file manager, move the CURRENT firmware file somewhere else (I moved it to the DOWNLOADS folder), copy the name, go to the NEW firmware and change the file name to the name just copied from the CURRENT firmware. (For example, the current firmware was called "2.zip ", and the NEW one was called "1.zip ". Now the NEW one should be called "2.zip ".

Return to the firmware update window and click "Extract" or "Install".

Wait for the process to complete. The device should reboot at the end (or suggest that you restart it - agree).

Congratulations! You are on Oxygen OS!

Remember! There is no ESIM in the Chinese version. But 2 physical SIM are working properly.

Remember! Follow all the steps carefully. Everything you do, you do at your own risk.

Good luck!

If something is unclear, ask me, and I will try to help.

UPD 1.

If the update is stuck at 0% or you get an unpack error, please check the integrity of the downloaded archives. Most likely something went wrong during downloading or when you edited parameters in *.txt files.

Try to download the archives again. Also try using WinRar to edit files without extracting the archives.

UPD 2. Thanks to @m.s.hamza, we know that if you did something wrong, or were helped by someone not in this thread, you can lose the imei. To get it back, just clean all data (settings - find - remove all data) and then roll back using the rollback firmware.