That website is interesting, but maybe not as significant as it initially appears.
In some sense chardet doesn't explicitly support Python 3.7, but it's packaged for it in Debian Stable. I wouldn't expect any problems.
more-itertools is listed in white simply because it doesn't use any granular version classifiers on PyPi. It only has a python_requires setting, which is authoritative.
It's plausible that every single package on that page supports Python 3.7 in practice.
https://pyreadiness.org/3.7/