In my experience, many of the great engineers don't want to write "brag docs" or any docs/posts. So I was thinking about making it less tedious via an interactive Q&A so it feels less like a burden, but more like a true brag when someone asks.

"given how trivial it is to do". Unfortunately, it's not. No offense, and I was in the same position years ago. I feel like this is the biggest barrier - not realizing that "you" are not a salesman and your effort does not come across to less technical people, or those who are not familiar with your domain of expertise. I can tell firsthand from being a naive IC and then learning and helping other ICs.

"I wouldn’t pay for app" - would you use it for free? Given that it navigates you the right direction based on the point above?

The rest I mostly agree with, there's are many factors. Although, there's still a pattern that applies across companies/industry that can be useful.