Do pokemon natures matter for a normal playthrough?

ignore it unless something feels off. the only time it really bites is a slow nature on a sweeper, like a Brave nature on something you want to outspeed things with. Sword/Shield and Scarlet/Violet have mints if you want to change it later anyway.

Not really. It's +10% to one stat and -10% to another, you'll beat the story with any nature. Only worth caring about for competitive or a hard nuzlocke.