Try to make the writing exercise less about yourself. Who is the documentation for? A new hire or someone else whose never worked with this product before. Try to make the documentation exercise more about them.
If you were asked to ramp up on this product, what information would you want to know? How can you help others be successful?
A good technical leader isn’t just about to churn out code and make trade offs in design. A good technical leader is able to take a complex space and drive clarity for others.
You have an opportunity to disambiguate a topic here to help others. You get to choose what’s the right level of detail to provide.