This is a Wild Area event held by Sword and Shield. All slots of this event hosts Milcery with the Gigantamax Factor.
At time of writing, there is no other way to obtain Ribbon and Star sweets in-game, without Mystery Gift or Max Raid updates.
Thus this max raid update is one of the only times players can obtain those items.
This event also has an increased chance of landing a Shiny Milcery; players have a 2% chance of landing on a guaranteed Shiny, only at the 5 star tier.
To import these files into your save, use PKHeX's block importing function. Our tutorial should guide you through it.
Our first post of this page contains some data relevant to the importing stage.
There's info and some common questions regarding Wild Area Events here.
To see other Wild Area Events, here.