My https://github.com/jab/bidict/community page is also showing that a Code of Conduct is missing, but you can see I have one at https://github.com/jab/bidict/blob/master/CODE_OF_CONDUCT.rst (namely the Contributor Covenant, which I’ve been using ever since it came out several years ago).
My Code of Conduct in fact exactly matches the one GitHub suggests that I use when I load the https://github.com/jab/bidict/community/code-of-conduct/new?template=contributor-covenant page – same version exactly (namely version 1.4). The only difference is that I use the .rst rather than .md format, so that I can include it as a source file for my documentation website, which is powered by the very popular Sphinx documentation tool, which uses .rst as its native format.
If the mere .rst rather than .md extension is in fact the only reason GitHub is failing to detect my code of conduct, note that according to the 6,493 current search results for the https://github.com/search?q=filename%3Acode_of_conduct.rst query, this likely affects many other projects. But if this is the cause, it should be easy for GitHub to fix.
Hope this helps, and that this can be fixed at some point before too much longer.