Musical instruments
You don't have to become the next big name in music to get something from taking lessons. One research indicated that giving preschool-aged children just 75 minutes of music instruction each week for 12 weeks significantly increased their IQ scores.
A more recent 2021 study also revealed that teaching instrumental music to children aged 6-7 may improve some executive functioning. Even adults can gain from music training. According to a different study, the duration of musical practice in adults and executive functioning were positively correlated. So it's a good idea to choose the musical instrument you've always wanted to learn that might increase your IQ. However, there are benefits to just listening to music. According to a 2018 study, a musically-enriched environment could improve children’s verbal IQ scores.