My thought is that one can extrapolate a lot about a project from particular discussions. However, my exposure to OSS is quite limited to the projects close to me.
Can anyone share canonical public discussions that demonstrate project values and culture? Perhaps that would belong in Erdos's "book" for that project or those that you find yourself referring back to.
... and/or set of values: https://kubernetes.io/community/values/
There's also a lot of open source guides here https://todogroup.org/resources/guides/ that may help you if you're looking at building mature open source projects.