Ok the heading doesn’t make sense but in Pokémon Sword/Shield there are 2 people giving us pikachu or eevee depending on the version we played earlier. I played Sword and Shield first so when I buy Let’s Go and complete it, will I still be able to get the pikachu or eevee?
Yes, you still will be able to get your special Pikachu/Eevee.
You can collect it from talking to the boy in the Wild Area Station.
You can also find Eevee and Pikachu in the wild of route 4.
Hope this helps!