The advantages of self-publishing on Amazon kdp (kindle and/or softcover print on demand) include total control over the project and receiving 100% profits from the book. Total control also means the author assumes the burden of completing all the steps which used to be done by the publisher. This includes editing and proofing as well as design and formatting.
Amazon provides tools and instructional videos but there are some (expected) issues. It is easy to get the manuscript almost right but difficult to get it completely right. The same applies to the formatting and jacket. If you use the generic jackets you can get the jacket looking good after watching videos and tinkering a bit.