All owners of Android smartphones know that updates are a hard subject to talk. Most of the devices with this operating system just do not receive them. Even smartphones with guaranteed updates have very limited maintenance period. Fortunately (or not) you can also download and install unofficial ROMs which will make your old phone more modern thanks to the new version of Android.
Phones with the official support from Google and all Android updates were manufactured by several vendors as the Nexus series. Unfortunately, the giant fairly quickly forgot what they have promised and a lot of Nexus devices (including Samsung Galaxy Nexus) did not receive the Android Nougat update. Fortunately, for these outcasts always remain unofficial ROMs.
The new ROM for Samung Galaxy Nexus is called Unlegacy-Android and it is based on the Android 7.1 Nougat.
The files were placed on the XDA-Developers forum. Of course, as always in case of unofficial software, the ROM may contain very serious errors and therefore it is not recommend installing this by inexperienced users. To be honest, you can simply brick your smartphone if you do not know what to do. Android 7.1 brings, among others changes to the settings, the notification panel, application shortcuts, new emotes etc. This is some modernization for the smartphone, so I am not surprised that everyone wants to have this.