The documentation gives instructions, how to debug an application on embedded devices (boot2qt). It doesn't say, how to debug Qt itself, especially qtbase.

This internal wiki contains more information about development and debugging. However, it relates to Qt 5.9, and the instructions given do not work. Especially instructions how to debug and develop qtbase for embedded Linux are missing.

While this may be irrelevant for users, we can't expect community contributions and even internal bug fixes without proper and up-to-date documentation.