[OnePlus 12] LobaApex:
Guys here is the breakdown of my experience in flashing OxygenOS on OnePlus 12 (16/1tb cn version). I ran into some errors, so I hope this might help some of you who aslo ran into them.

Ill write error troubleshooting that I encountered throughout this process after all of the steps!

This is the order in which I did the flashing (might be wrong, but in the end it worked for me)

First part is downloading files for flashing:

- Drivers for oneplus / oppo

- ADB Platform tools (if you dont have them already)

- FTH .img files for flashing

- SuperZip script for flashing

Second part is setting up my device:

- Backing up stuff if your phone was not new or straight out of the box

- Enabling developer options

- In dev. options enabling OEM Unlocking, USB Debugging

- To actually enable OEM Unlocking, you will need to restart your phone once

Third part is flashing process:

- Everything regarding this part was explained in the OP, but ill go over it again

- First thing you need to do is check that your device is visible on PC, either in Device Manager or running command "adb devices"

- If you see your device, or rather if the list is not empty when you run that command, youre good to go

- Now we need to go into the Fastboot mode by turning off the phone, then holding power key and volume down (-), or writing a command "adb reboot bootloader"

- Now we are in the Fastboot mode

- From this point we run command for unlocking a bootloader "fastboot flashing unlock", a screen with warning message will appear, use Volume buttons to scroll down to "Unlock the bootloader" and confirm selection with power button! THIS OPERATION WILL WIPE YOUR DATA SO BEWARE

- When you unlock bootloader, phone will restart, you will see orange text that says "Orange state....", your phone will boot into initial setup

- Turn off your phone by pressing Volume up (+) and power button

- Turn it back on into Fastboot mode by holding Volume down (-) and power button

- When we are in Fastboot again we are good to go onto the next step

- We previously downloaded FTH folder for your region (I used global one), my folder structure was like this:

- bin

- driver

- FTH

- Flash_All_SupperZip

- ROM_properties

- bin folder contains another FTH folder with adb tools extracted inside

- driver folder have the OPPO drivers (this is optional)

- FTH folder has .img files for flashing

- So when you fill FTH folder with .img files, we are ready to run Flash_All_SupperZip, phone has to be in Fastboot mode

- Start the script, if your drivers are okay, you will be asked to press any key to continue

- Second stop of the script is to "Format data", just press any key and wait for it to finish

- Third and last stop is when you get to the end and it says that "FORMAT DATA - ENTER CODE", your phone will be turned on into the initial setup page where you see "Hello"

- Turn off your phone by holding Volume up (+) and power button, and simply scroll down to shut down, then after the vibration, turn your phone back to Fastboot mode by holding Volume down (-) and power button

- In Fastboot mode, select Recovery by pressing down Volume key and selecting it with the power button

- In recovery mode, select English language, then Format Data, you will get a promt with the code that you need to type in manually via touchscreen (you don't need volume and power buttons) and click on "Confirm" or "Format data" when asked if you want to format it

- After that your phone will restart and you can proceede with the initial setup

- Upon reaching home screen youre good to go

Fourth part is locking back bootloader (optional):

- You should enable Developer options again like in the first step

- Since your bootloader is unlocked, OEM Unlocking is enabled and grayed out, USB Debugging needs to be enabled again

- Plug in your device into the PC again, run commnad "adb reboot bootloader"

- When rebooted into Fastmode, run commnad "fastboot flashing lock"

- Use Volume keys again to select "Lock the bootloader" and confirm your choice with power button

- After that your phone will restart again, and there shouldn't be Orange text again on your booting screen

- Thats pretty much it

- Note that if you want to unlock bootloader again, your data will we formatted

Errors that I encountered while doing this:

- First one was unrecognized drivers:

- I've got to the third step aka flashing, when I ran the script, my device didn't show up on the list

- Solution: Open Device Manager on PC

- Under "Other devices" there should be a "ossi" device that was not recognized, thats your device

- Choose an option to update or install driver

- Select "Browse my computer for drivers"

- Select "Let me pick from a list of....."

- Select "Android Phone" from the next window

- After that there it should be two small windows, one that says "Google" and "Oppo", the other one with the driver suggestions

- Pick "Oppo" on the left window, on the right window pick "Android Bootloader Interface"

- After doing so, try running script for flashing again, it should work now

- Second one were bad flashing files:

- I completed flashing with script, no errors, wiped data via recovery, then on the initial setup i got stuck on "Just a sec..." screen.

- One more sign that the flashing was bad is that I didn't get keyboard prompted out when I tried to enter password to connect to a WiFi

- Solution: I reflashed OxygenOS again, this time with different FTH .img files

- Steps for reflashing are the same, you boot your device into the Fastboot mode, run the script for flashing again, format data again with recovery

- After that phone will reboot again into the initial setup, this time you should see the keyboard prompted out when trying to type WiFi password

- Phone should work now

Huge thanks to @Canuck Knarf for troubleshooting second error with me.