Hello BrutusG,
thank you very much for reaching out to the CRM Forum. I did not exactly understand, if you are facing the issue, that no entites/tables and attributes/fields are listed to choose at your gallery datasource, of if you want to get a list of all your (custom) entites and attributes retrieved, to list it at your gallery/CanvasApp itself.
So please let me explain, in case you cannot see the entities listed, for selecting at DataSource at your Gallery, please make sure, you created the CanvasApp at your particluar CRM/CDS environment selected, and not the default environment:
If you want to list all the entites and attributes of your CRM environment, there is no specific Table, at which all entities are listed and I also think, there is no out-of-the-box PowerPlatform Function availalbe, to do this.
But you can get the metadata and information about all your entites/tables and the attributes, using the WebAPI at your CRM/CDS environment. So it should be possible, you create a Flow or an Azure Function, which retrieves the WebAPI data (using http request or REST), and return the data back to your Canvas App.
To do so, you can use the WebAPI functions for EntityDefinitions, like:
https://<org>.crm.dynamics.com/api/data/v9.1/EntityDefinitions?$select=LogicalName,DisplayName
https://<org>.crm.dynamics.com/api/data/v9.1/EntityDefinitions(LogicalName='account')/Attributes?$select=LogicalName
This will return in oData v4 Format/JSON all the LogicalNames and DisplayNames of your environment, and the second request, will list all fields/attributes of the "account" entity for example.
If you are further familiar with the WebAPI, you see, you can also add also different fields, like checking, if it's a customizable entity with the field IsCustomizable, or using the filter for IsCustomizable/Value eq true (https://<org>.crm.dynamics.com/api/data/v9.1/EntityDefinitions?$select=LogicalName,DisplayName,IsCustomizable&$filter=IsCustomizable/Value eq true)
For more information about the WebAPI function and a possible way, to do so with Flow, please have a look at the following URLs:
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/webapi/retrieve-metadata-name-metadataid
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/webapi/query-metadata-web-api
https://powerapps.microsoft.com/en-us/blog/return-an-array-from-flow-to-powerapps-response-method/
I hope, this information will further help you with your issue.
Thank you very much, please let me know, if you have any further questions on this or if this resolved your issue, have a nice day and please stay further healthy.
Best regards
Daniel
