Legendary, Mythical, and one-off Pokémon (such as Type: Null) cannot have their QR codes shared.
You can also share your own QR codes by accessing a Pokémon’s Pokédex page and viewing its code. Individual forms, different genders, and even Shiny Pokémon have separate QR codes. Much like in Pokémon Sun and Moon, this allows you to check the locations of Pokémon you scan! However, there are limitations the QR Scanner only allows you to store up to 10 scans of different Pokémon, and a scan regenerates once every two hours. The QR Scanner is a feature that allows you to add ‘Seen’ information for Pokémon not yet encountered. The available Pokémon have changed: while the Johto and Unova Starter Pokémon are no longer around, now you have the opportunity to capture the Kanto, Hoenn, Sinnoh, and Kalos Starters! QR Scanner Point and scan! The Island Scan feature, which is all about scanning QR codes for the chance at a rare Pokémon, has returned to Pokémon Ultra Sun and Ultra Moon. Pokémon Ultra Sun and Ultra Moon Version Exclusives and Trades.Pokémon Ultra Sun and Ultra Moon Alola Dex: Locations and more!.Pokémon Ultra Sun and Ultra Moon Island Scan.The Best Pokémon for Pokémon Ultra Sun and Ultra Moon.