Hi Richard Warren,
Thank you for reaching out to us on Microsoft Q&A forum.
Once you created the collection, take a blank screen and add the data table, if you do not find the collection under the data source as per the below screenshot.
Kindly follow the alternative steps.
Step 1: Select the data table and in Power fx give the collection name as per the below screenshots.
Step 2: After giving the collection name select the data table and add the fields as per the requirements. Kindly refer the below screenshot.
If you are still facing any issue, please let us know in the comments. We are glad to help you.
If the information is helpful, please Accept Answer so that it would be helpful to community members.
Thank you.