You will probably need to use a combination of endpoints and external processing to get the report that you’re looking to generate.
To get a list of all repositories that a given user has explicit permission to access, you will want to use the List your repositories endpoint. This endpoint will give you a number of open issues, but not a number of open pull requests.
To get the number of open pull requests, you will want to go through each repository and use the List pull requests endpoint using “open” for the state parameter.
You could also probably use the GitHub GraphQL API for this so that you’d only have to make one call, but that will take some experimentation to get exactly what you’re looking for.
Hope this helps!