This Magearna has the TID hacked to be Shiny, nothing changed apart of that.
At the time this post is made, this Pokémon is marked as legal in PKHeX and it is currently unknown if Home can assign a Shiny TID for the Magearna. However, there are no report of a legitimate Shiny Magearna yet and Sword / Shield servers refuse to trade this Pokémon, so i assume it's definitely Shiny Locked.
This Pokemon is now correctly shown as illegal by PKHeX.
The original one is downloadable here: