I am not a native English speaker, but I usually use the word writer and author interchangeably. Possibly the word author would maybe refer to a more specific writer of a referenced book or something, but that’s about all I can think of as a difference between the two. Is it ok to add the synonym of writer to this vocabulary? Or am I missing a crucial difference?
The primary difference between them is that a writer is the one who does the writing of a book, script, article, etc, whatever it may be, and an author is the one who comes up with and formulates the idea(s) for whatever is to be written
Often times the author and writer are the same person, which is why it’s seen to be used interchangeably
Author specifically refers to writing books, articles, etc. Whilst a writer is more generic that inclues things like songs where you wouldn’t call them a song author but a songwriter.