He already played the guitar before the scene of his character Eddie Munson playing Metallica's "Master of Puppets" in Chapter Nine: The Piggyback (2022), but he still bought a guitar and practiced on it for months before filming the scene.
[On an Interview with The Liverpool Echo. Telling the story about how his mom told her sisters he got the Stranger Things role] When my mum called them and told them I've got this Stranger Things job, my auntie went mental and my mum went 'oh, so it's a big deal then, is it?' and she was like 'are you messing?