SD-6 says the __cpp_lib_to_chars macro is defined in <utility>,
because that's where P0067R5 added std::to_chars and std::from_chars.
However, not long after they were moved to their own header,
<charconv>. The feature test macro should be defined in there, not
<utility>·

No implementation shipped with them in <utility> so there's no reason
to say the macro is in that header for implementations conforming to
P0067R5 and in <charconv> for implementations conforming to P0682R1,
we can just fix it to be <charconv>.

The C++ working draft is being amended by https://wg21.link/lwg3137
and SD-6 should be changed too.