OTA failure may include below phenomena:

OTA update failed

1. Check if the handset already root or not, please back up all the data, clear cache and flash to the latest OxygenOS version;

2. Check if any third-party security software was downloaded when the OTA upgrade failed. If so, it is recommended to delete the third-party security software and back up all the data, clear cache and flash to the latest OxygenOS version.

The system shows update available after OTA was successfuly install

We suggest to switch to other Wi-Fi or use another mobile network for re-downloading the OTA; if it fails again, you could download through PC via downloads.oneplus.com and copy it to a device for updating.

Note:
Please back up all the data, clear cache before installing the latest OS version.