[Answering to get this off Unanswered]
Yes, the Shiny Charm is available in Legends:Arceus.
Here's a screen grab from YouTuber Sloppy Gaming:
![](https://i.postimg.cc/V5ybfL7S/Screenshot-20220131-151252-You-Tube.jpg)
As mentioned, more popular YouTubers have also obtained it.
According to Serebii, it can be obtained by
getting Research Rank 10 with all 242 Pokémon within the game.