[OnePlus 7 Pro ROMs, Kernels, Recoveries, & Other D] RfBob:
You're absolutely right. I modified that bit.

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As there still seems to be some confusion I came up with a summary. Credits go to @mauronofrio and @tithokan and @acervenky. I am only contributing this summary. They did the whole work behind the scenes. So buy them a drink or something. Thanks/Rep is appreciated nontheless ;)

Remember that this procedure is breaking your wifi connection if you do not flash a third-party kernel afterwards OR start with the right boot image. E.g. if you are on GM1913 9.5.5, use the one supplied below and you will be safe.

If you are unable to find your specific version below you can still flash a third-party kernel afterwards or just patch the image yourself as pointed out by GoodSoul here.

BOOTLOADER UNLOCKING:

1. enable Developer Options: Phone settings -> About phone -> tap “Build number” 7 times -> Developer options appear in system settings

2. enable Debugging Mode: Phone settings -> System settings -> Developer options -> enable USB Debugging

3. enable OEM Unlocking: Phone settings -> System settings > Developer options -> enable OEM unlocking

4. download ADB Tools and extract them to c:/

5. open a command window (WINDOWS + R -> "cmd") -> type "cd c:/platform-tools"

6. connect OnePlus 7 Pro to the computer with USB cable -> in cmd type "adb devices" -> on phone: grant acces to your pc and check to keep this setting

7. type "adb devices" again -> the status should have changed from "unauthorized" to "device"

8. type "adb reboot bootloader" -> phone reboots to "fastboot mode"

9. type "fastboot oem unlock"

10. navigate to “Unlock the bootloader” option by using the volume button and select it with the power button

11. YOUR DEVICE WILL NOW BE WIPED AND FACTORY RESET! YOU WILL LOSE EVERYTHING STORED ON THE PHONE!

12. let it boot in patience

13. (optional) set it up

ROOTING:

1. Download: OOS 9.5.4 Patched/OOS 9.5.5 Patched and rooted (credits go to djsubterrain) [EU Version/1913] OR OOS 9.5.4 Patched [Global | Indian Version /1917 | 1911] (THREAD)

2. Download and install Magisk Manager v7.2.0 on OP7 (you propably need to allow unknown sources in developer options or/and grant access to the browser you're downloading the file with to your phone.

3. repeat steps 5 + 6 +7 + 8 of BOOTLOADER UNLOCKING

4. type "fastboot flash boot boot_patched.img"

5. (optional) cmd told me the following: "fastboot: error: Failed to identify current slot" - > I got this solved by navigating to "restart bootloader" with the volume keys and selecting it by pressing power. After this the command, as seen in #4 worked. (i did not have to mess with active slots or else - maybe this is just me)

6. type "fastboot reboot"

7. let it boot in patience

8. open Magisk Manager -> select install -> select install again -> direct install (recommended)

9. press "reboot"

10. you are rooted

INSTALLING TWRP:

1. Download TWRP 3.3.1-20 Unofficial Installer by mauronofrio to your phone OR pc and move it to your phone (Thread)

2. open Magisk Manager -> press menu toggle -> select "modules" -> press "plus"

3. press menu toggle -> navigate to the place you stored the recently downloaded TWRP (by phone: propably "downloads" / by PC: propably "internal storage"/"root directory")

4. selecting it starts the flashing process of TWRP

5. DO NOT YET REBOOT IF YOU WANT TO KEEP ROOT!

6. go back to Magisk Manager and install magisk (see "ROOTING" #8)

7. reboot

8. you do now have TWRP and root

MISC:

How to maintain root on new OTAs