Quoted By:
>"During your adventures in the Paldea region, you may find black crystals that look different than the ones you ordinarily approach to take on a Tera Raid Battle. The Pokémon you’ll face at these black Tera Raid crystals are much stronger than those that appear at ordinary Tera Raid crystals, and defeating them can net you rewards that are even more exciting than usual!"
>"You’ll be able to take on Tera Raid Battles at black crystals after completing certain postgame events."
Here's your postgame bro