One of the rarer Pokémon in Pokémon: Let’s Go, Pikachu! and Let’s Go, Eevee! is the Water/Ice-type Lapras. Fortunately, for those of you who don’t have the patience to find one in the wild, there is a much easier way to obtain it.
During the games’ main story, there will be a section where the player must storm the Silph Co. building, which has been taken over by Team Rocket, in an attempt to free the company from the villainous group’s grasp. Once inside the building, take the elevator to the fifth floor. Here, travel left a little bit until you find the Team Rocket Admin Archer and a Team Rocket Grunt. As you get close, your rival will appear and the two of you will battle the two Team Rocket members. After defeating them, you will receive the Key Card, which allows you to open previously locked doors in the Silph Co. building. Now take the elevator to the seventh floor. Wander around the floor unlocking doors until you find a man sitting in a red chair. Talk to him and he will give you a Lapras.
In the wild, Lapras appear on Routes 19 and 20, but they are extremely rare. You can try to increase their spawn rates by using Lures, Super Lures, or Max Lures, which call out rare Pokémon, or by getting a high Catch Combo by catching a large number of the same Pokémon in a row.