Search for PRs in dotnet/runtime by a particular user

PRsByUser.graphql

{
  search(query: "repo:dotnet/runtime is:pr author:stephentoub", type: ISSUE, first: 100) {
    edges {
      node {
        ... on PullRequest {
          title
          url
          number
          createdAt
          state
          author {
            login
          }
        }
      }
    }
  }
}

Visit https://docs.github.com/en/graphql/overview/explorer to try it out.