I haven't personally run a notebook in Databricks but from the thread that you linked it sounds like Databricks as an API layer that can be connected to and interacted with via a REST API resource in Retool.
It sounds like you need:
Base URL
Set headers with content type(Same as in link) and Bearer [your_token] which would be unique to you
Then you should be able to rest the resource connection and see if your token and url are valid. Have you been able to get your URL and token into a REST API resource and test the connection?
If you get an error at that step let me know and share a screenshot of the error so we can try to troubleshoot.
Once the resource is connected you should be able to test out some queries using your job_id!