I haven't been able to find any, and automated tools out there don't seem to work too well as they're mostly made for REST not RPC. However, if you test out a script following the developer guides in the docs, you can figure out how they work and what fields are available. I used App Script (Google) and Python to do this.

But if you're trying to get documentation for functionality as opposed to fields, I don't know how you'd do that and I'd love to find out.

I see what you mean. There are no guides unfortunately. What you can do instead is enable developer mode and try to replicate the flow of what you want to do with the api on the front end. Hover any button and it should display info about the method/endpoint it calls. Field names will also show when you hover over them

Other than that you would need to be more specific about what you want to do for more assistance or get someone who understands python and Odoo to go through the source code.