I had a tiktok page and my book was due to people asking me to make a book based on my tiktoks. So I made the book and told them when it was done. I don't consider this advertising.
So to be fair, you made something you knew people wanted. This is not advertisement, but it is surely marketing. (Marketing starts before you built the product)
I had such a difficult time getting word out to the 300k people about the book, I would be glad to let even 10% of them know about it to this day. I still have 200 copies lying around and sales are dead. At most I was able to let a few thousand people know, if that.
Please. Even 1% of 300k is a lot of free targeted advertising. And yes that's what it is, even if you don't want to admit it. It's exactly the kind of promotional bootstrapping that OP was asking about and you pretended you didn't have to do it until we dragged it out of you.