Linking the Polestar 2 to Google Assistant turned out to be more complicated than it should be. So, as a service to others who are looking to do this, here are the instructions that I ended up using to link my car to Google Assistant.

Go to the Google App on your phone.
Click on Settings
Go to Google Assistant
Click on Devices
Add Device
Link a car

Linking the Polestar 2 to your Google Assistant