In case of the OnePlus Nord OTA upgrades should have been offered from Android 10 to 11 and from 11 to 12, both are listed as completed at https://community.e.foundation/tag/development-updates .
OTA upgrades are only available on stable builds so far.
Are you on the stable or dev release channel? See [HOWTO] Give complete /e/OS version info easily for support, answers, comparison etc
That being said, informing oneself in the forum is a safe way to get to know supposedly available updates. An updater can malfunction, a notification might not be shown etc.
The build download pages mentioned in the manual install instructions can be used to look up new versions, too.