I noticed that no one has replied to this post. Have you found a solution to this issue since you posted it at the beginning of the month?
I got the solution to this one, It's a Proxy server problem.
The CORS proxy given in WDC documentation page of Tableau did not work for me I had to use another one corsproxy-https for my API and it worked.
But I noticed another one. There's no Union option below the tables for WDC data source, the only option is to join the tables.
Is there any way to make a union of two tables in Tableau when we use WDC as the data source