Starting from 5th June 2020, a serial code that allows users to redeem a Dynamax Crystal for Gigantamax Copperajah has been made available.
As far as I can tell, the event were announced in European countries, between going to Gamestop or GameMania between 5th June to some early date in July(prior to the DLC launch). (link)(link 2)
The changes done to the Dynamax Crystal populated dens was first observed here (June 02, 2020),
however it's status of it being an official event was not known (think Unreleased Gmax Butterfree Event).
A wonder card for the Dynamax Crystal was later uploaded to the BCAT (June 03, 2020)
It later received confirmation of being an official event (June 05, 2020)
As of time of writing, this event is the only way to get Curse on a Copperajah that can Gigantamax without breeding move transfers, from event raids. This events also has a certain fixed IVs