The latest official firmware available for the Note 5 is Android 7.0 Nougat. Even without Oreo, Samsung continued to provide maintenance patches, with some versions receiving stability updates as late as . Official Version: Android 7.0 Nougat. Latest Security Patch: Typically August 2018.
You can find official firmware files for manual flashing on sites like SamMobile or IMEI.info. How to Get Android 8.0 Oreo (Unofficial) samsung note 5 software update 8.0 download
Since Samsung did not release an official 8.0 download, the only way to run Oreo on a Note 5 is through . These are community-made versions of Android that often bring newer features to older hardware. Popular Custom ROM Options: The latest official firmware available for the Note