This is a Wild Area event held by Sword and Shield. This event does not appear to host any Gigantamaxes.
This event give players a chance to encounter a shiny Grapploct from 5-star Raids.
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.