In 2016 I wrote a short book about my experiences in Vietnam, about 135 pages (printed on one side in notebook size). I proof read it twice before printing it and thought I found all the errors.
Wrong.
Over the next 2 years as I printed more copies I would proof read it each time, and I found more mistakes & typos every time. I think I found only two or so the last time, and I'm not doing it again.
The lesson here is that it's almost impossible to proof read your own writing and find all the mistakes. Apparently your brain will 'skip over' the errors just as it did when you first made them. But maybe it's just me.
For the record, I made 2 mistakes typing this post and fixed them. But no guarantees that I didn't miss any.