This Pokémon is a rare variant that is capable of Gigantamaxing, and can only be obtained via Max Raid Battles in the Wild Area.
While not always available for capture as it could not be found in a den in the Wild Area, an event from February 07, 2019 to ? made it more commonly found, by having it appear in dens normally not associated with it.
The Amped form can be found by Sword hosts, and the Low Key form can be found by Shield hosts.
To be able to encounter this, user's Switch must be connected to the internet, with the Mystery Gift>Get Wild Area News option used during the event period..
Alternatively user must have connected to the internet and redeemed a Mystery Gift during the event period.