Seems like Pokemon Home is giving shiny(?) Magearna, as a gift when you complete 890 full pokedex at there. I don't know this is a new form or a kind of shiny. Perhaps we may need to include Pokemon Home gift distribution later..
Just want to comment.. I checked quickly and found some Pokemon has several years old dates(captured, etc..), definitely before the release of Sword & Shield. Make no sense at the moment, because we can't bring any previous Pokemon officially until the release of Pokemon Home in 2020.