Source:Android Authority
Warning ⚠️
I)DO NOT DOWNDRADE TO OxygenOS 13 AFTER UNLOCKING BOOTLOADER
II)BEFORE LOCKING BOOTLOADER MAKE SURE TO UNROOT IT
III)YOUR INTERNAL STORAGE WILL BE WIPED
- Turn on Developer option
Info! To enable developer option open settings>About Phone>Version> Tap version no 7-8 times. Enter your Password/Pin/Pattern if prompted - Go To About Phone - Tap on Oxygen OS
- Tap 4 dots at top and select "Local Install" and select downgrade file.
- Tap Install
Warning!
Your phone will reboot and all your data will be erased.
Link to the thread:
Oneplus CommunityLink to OOS 13.1.1.224: Download
Video Guide:
Credit: NordCE3 Community
Pranish