Usually, the possibilities to get an income from publishing a book are overestimated, and the difficulties with selling books (storage, distribution, payment, etc.) are underestimated. See also these previous discussions:

https://www.researchgate.net/post/Self_publishing_is_worth_it_in_terms_of_my_future_career/1

https://www.researchgate.net/post/Which_is_the_best_and_reliable_platform_to_self_publish_ebook_free_of_cost/1

https://www.researchgate.net/post/Have_you_had_experience_with_self-publishing_a_textbook/1

https://www.researchgate.net/post/Publishing_books_on_Amazon/1

https://www.researchgate.net/post/How_to_get_rich_from_writing_a_book/1