Hello natalieportman,
Thank you for your advice. Of course, the files cppreference-doc-en-cpp.qch and cppref.qch are included – as you described – and are located in /usr/share/qt5/doc/.
With F1, I can only get help for const (!) and other keywords like int, etc. However, for constexpr (!) a message appears stating that no documentation is available. However, if you open cppreference-doc-en-cpp.qch, for example, via the Help menu item and look under Keywords, there is indeed a constexpr entry with a link to the manual page. In my opinion, there is an indexing error here.
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