I can run the existing queries with or without parameters. I tried some POST calls to create a new query in Data Explorer without using the Admin console, but failed. Is there a method to create/delete a query in Data Explorer?
It’s certainly possible. You can Reverse engineer the Discourse API to do anything with the API that you can do in the UX.
If you’ve tried something that didn’t work, you can share your code so that others might make suggestions.