There are several methods for updating OnePlus phones. However, if you're logged in as root with TWRP, one of them is the best option. It works like a charm and retains its root status after an update, and you do not even need to connect to a computer like you did on the first root installation.
This method is pretty simple. All you have to do is manually download the OTA update file and install it over the existing TWRP recovery environment. Then you need to flash TWRP and Magisk again. You have to do things in a specific order, but follow these instructions and you will be updated in no time.
Step 1: Download the Oxygen Updater App
The Easiest Way Manually When you download OTA updates to your OnePlus device, use the Oxygen Updater app from the Play Store. You can download the latest OTA.zip file for your device without having to search online. Typically, even the firmware files are saved before they are uploaded to the OnePlus download site.
Step 2: Perform the Oxygen Updater setup
After the Oxygen Updater app has been installed using the link above, open it the main screen so you can get started. Scroll through the welcome page by swiping left twice. Then on the "Choose Your Device" page, make sure that "OnePlus 7 Pro" is selected. If not, tap the arrow and select the desired option.
Swipe back over the "Root Access" page and learn how to work with root privileges. Tap "Close" and then "Grant" to Magisk's superuser request to provide root access to Oxygen Updater for even more features Pro without root loss – no computer required ” width=”532″ height=”532″ style=”max-width:532px;height:auto;”/>
Now make sure on the "Select Update Method" screen, the "Complete Update" option is selected before proceeding. Tap the arrow again and select the correct option. Swipe left one last time until the last screen appears, and then click the "Start App" button at the bottom to begin downloading the OTA update file.
Step 3: Download the OTA Update
After the Setup is complete, you should be sitting on the main screen of the Oxygen Updater app. If an update is waiting for you, the message "New system update available" appears immediately along with the details below.
Scroll to the bottom of the screen and tap the "Download" option for Start downloading the entire system update. Grant the required media permissions when prompted by tapping Allow. The download will start automatically.
Note: If you use a VPN, you may occasionally need to try another server or temporarily disable it for the update to get through properly. Otherwise, you may not be waiting for a network connection. So keep an eye out for future updates.
Step 4: Download Magisk
Striving to Maintain Your Root Access As an OTA update, you may have already downloaded Magisk and you're ready to go. If not, click on the link below to proceed to the next section. Make sure you download the latest version of Magisk instead of Magisk Manager.
Step 6: Install the OTA Update  At this point, your device should be in the TWRP main menu. From here, tap "Install" and locate the previously downloaded OTA file. By default, the Oxygen Updater app drops it to a specific location, which is itself outside of any other folder. This is called the root directory of your storage and makes it easier to find.
Tap the OTA file once to put it in the installation queue. Make sure the "Inject TWRP after installation" option is selected, and then start the Swipe to confirm Flash sliders to begin installing the system update. Because the full system image is more than 2 GB in size, it may take some time for the installation to complete. It seems to be frozen at the end of step 1, but eventually moves on to the next step.
Then tap the Start button to return to the main screen. Select "Restart" and then "Restore".
Step 7: Flash Magisk & Reboot System
Now you have the OTA Update and TWRP on Your system requires Magisk for your root access. After rebooting, go to your "Download" folder to restore and install the Magisk file as you did the first time by dragging the slider. Once the Magisk installation is complete, you can tap the Restart System option to restart Android as normal.
You now have the latest version of OxygenOS, your custom TWRP recovery is intact, and your root access still exists. As a bonus, you will now receive your system update notifications from the Oxygen Updater app. This not only makes it easier for you as root user to do the work, but you can also skip the slow rollout process. Immediate updates for everyone!
Cover image and screenshots of Stephen Perkins / Gadget Hacks