I haven't been up to date with Pokémon since Silver.
So you used to be able to transfer your Pokémon from earlier games (e.g. X/Y) to your new game (e.g. Sun/Moon) after completing the new game's League? And with Sword/Shield that's no longer possible?
You can only import pokemon from the regional Galar dex and you can only trade between Sword and Shield back and forth.
We dont know how many are included the Galar dex yet tho.