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The cover of the book was matte, I read it around 2017, it had a story about a black dot. The dot grew and eventually killed the narrator. It had illustrations of the dot as it grew

Sounds like blot by Gahan Wilson, aka *

It's collected in these books - The Cleft and Other Odd Tales is one of them.

Naomi, I notice your request is in a Solved folder. What is the title and author of your book?

My first thought was The Sun Dog, a short story by Stephen King in Four Past Midnight.

No response from Naomi, moving to Solved.