You've been bamboozled
-Top commenter
Don't feel bad though, as you weren't the only one fooled by this though. As you can see in the Reddit post, other people got similar information that Giratina could be found in Area Zero via an IMDb article. The article was even apparently typed on 12/3/2022! So yeah, the article is fake.
Unfortunately, the only way to get Giratina in S/V is to transfer it into Scarlet and Violet. I even checked a couple sites such as Bulbapedia and Serebii and both websites had similar information. I also checked the list of returning Legendaries in the Indigo Disk, and Dialga, Palkia, and Giratina weren't on the list.
Sorry if this isn't what you wanted to hear, but I hope it helped nonetheless.