Magic Static in Singleton Template
Your test code doesn't match your test output. &quot;Test.cpp&quot; isn't even valid C++ code!
How does your massive amount of code do anything significantly different from the following eight lines?
template&lt;class T&gt;
struct Singleton {
    struct Token {};
    static T&amp; getInstance() {
        static T instance(Token{});
        return instance;
    }
};

Example usage:
struct Widget { explicit Widget(Singleton&lt;Widget&gt;::Token); };
Widget&amp; example = Singleton&lt;Widget&gt;::getInstance();

As for why the &quot;thread-safe statics&quot; feature doesn't work on your freestanding platform, I would suspect it's because your freestanding platform doesn't support thread-safe statics. :)  Check the documentation for your toolchain to see how static variables are handled on that particular platform.