This library can help you with fetching flex queries from Interactive Brokers.
Simple call the library by passing your token and queryId:
... FlexResult result = new Reader().GetByApi(token, queryId).Result; ...
Or pass an already downloaded file:
... FlexQueryResponse result = new Reader().GetByString(content); ...
This repo contains all posts at dev.to.
This is the repo that creates the site you are looking at currently. So if you are interested in the technical background, this is the project you were looking for.