Magearna actually debuted in Steam Siege as Magearna-EX and a promo. Unless you are counting SM+ the main sets.Wait.... What???! Charizard GX??! I hope this Stage 2 GX will be good, pls.
The set name is super duper cool. Burning Shadows, huh? #ChandieReference
Wait. The only Gen 7 Pokemons that aren't give their debut in the main TCG set are Silvally and Type: Null, Giant Exeggutor, Alolan Marowak, Surfing Raichu (Yes, I know. He was in the Trainer Kit. You know what I mean), Magearna, and the Ultra Beasts. Maybe these will give their debut except Silvally, I expect Silvally to have it's own set.