According to this survey:

"The median income of full-time self-published authors in 2022 was $12,800 from books and $15,000 total from all author-related activities. Full-time self-published authors who had been publishing since at least 2018 reported a median income of $24,000 compared to $13,700 in 2018, a 76 percent increase."

Traditionally published commercial authors made about $10,000 more.

https://authorsguild.org/news/key-takeaways-from-2023-author...