I've installed the Arduino SAMD boards that the tutorial I'm following mentioned as well as the Arduino AVR boards and see no entry that says Adafruit Metro 328. In fact, the only Adafruit board I see is Adafruit Circuit Playground Express.
Here is my board list:
EDIT: for some reason the image isn't render (account age?)
Here is the imgur link to my boards list screenshot: https://imgur.com/a/aJ6Gmyb