I think that, for some adjectives, 是 is indeed used, but then the adjective is followed by 的. This is certainly true for colours and for shapes. For example: 她的头发是黑色的 = "Her hair is black" 她的脸是圆的 = "Her face is round" I don't know if there are any good rules for when this structure should be used.
Dope content like always! Small suggestion: mix the music a bit lower or use a less busy music. I think the neo-soul/mellow lo-fi is a lot better suited for educational videos because it makes everything less busy and organized for the ears. Or you can also remove the music during the information-heavy parts in the first place. For instance you could have music while you say "mistake 2: doing this instead of this" and then when you explain it there's no music. I dunno just some thoughts