I think the below resources are a good start.

This makes me curious: Do you have a specific goal in mind?

https://github.com/mozilla/pkipolicy

https://www.ccadb.org/

https://cabforum.org/

Indeed I do. We run a SaaS in a regulated industry, mainly in Germany. To receive and transmit certain payloads we need to use dedicated TLS certificates from a government run PK infrastructure (Search for "Smart-Meter PKI" if you are curious).

We want to become a sub-CA of this PKI and while we are aware of the policies of this specific PKI, we think that from an engineering or IT ops standpoint we can learn much more from web PKI CAs.