The self-publishing landscape has been transformed over the last 10 years or so. Before that self-publishing was equated with vanity publishing i.e. paying to have a book published because the author could not find a publisher.
There were some important exceptions. Royce's Sailing Illustrated was self-published, so successfully that a publisher picked it up and it has been in print for more than 50 years.
Now platforms such as Lulu and Amazon kdp present an opportunity for anyone to self-publish at no cost to the author.
I have just found a coarse but accurate observation:
'Self-publishing a shit book does not make you an author any more than popping a zit makes you a dermatologist'.
The most important concept is that, before you publish, you must have a story worth publishing.