If you ever wanted to live your dreams of becoming a famous songwriter, it is possible in The Sims 4, and here is how to do it.
How to write songs in The Sims 4
In short, to write a song in The Sims 4, you need first to raise your level with any kind of musical instrument to eight. You can do this by merely playing whatever instrument you want to use repeatedly. It could also help if your sim has some musical traits, as certain ones can make it easier to level their instrument skills.
Once you raise your skill to level eight, you will unlock the ability to write a song, and you can then write one by interacting with your instrument and choosing the option to do so. Be warned, though; you will have to spend 12 hours of in-game time to write and finish a song. But luckily, if you stop midway writing a song, you won't have to start over and can just continue again by selecting your instrument and sheet music in your inventory.
When you finish writing your song, you can then make some money on it by licensing it, but in order to do this, you will need to raise your instrument skill level to nine. After you reach level nine, you can then license a song by visiting your mailbox and selecting the "license song" option. Afterward, you will then receive money at the start of every day, as long as you have a song licensed. As a side note, you won't be able to license more than one song per week, but if you reached level nine on more than one instrument, you could effectively get around this.