Sometimes the 'Flutter Outline' tab says 'Nothing to show' while the editor has a valid flutter file open. Guidelines and syntax highlighting remain visible in the editor, so the outline seems to remain available.
@jacob314 and I have seen this intermittently, but we're not sure how to reproduce it. Navigating to another file seems to fix it.
Ref: flutter/flutter-intellij/issues/4659
If first opend, the Outline is black, but if click run app, then it's intermittently seen, seems something wrong with the deamon program.