I have a pikachu it lets go and I had got a light ball in sword, I wanted to put her in my sword so I could use her there. would she still have the great stats a regular partner pikachu would have? Or would they go back to normal?
The game-exclusive partner the player starts with cannot be traded to other versions of the games, nor transferred to Pokémon HOME.
So, Sadly, you can't even transfer it there :(. Source
EDIT:
You can, however, pick up a Gigantamax Pikachu from the train station in the southernmost portion of the Wild Area. It will have 6 max IVs, but it won't have the boosted BST that the partner Pikachu from Let's Go has. -KRLW890
That is completely true, you can do that.