Hi @Dan Jones ,
Welcome to Q&A forum!
I am a SharePoint support engineer, and your question is also related to SharePoint Development, which is not my field of expertise, so I add a related tag so that your question can be seen by SharePoint Development engineers. Regarding your question, I conducted research and testing and got the same results as you. However, I went to the SharePoint admin center to check, and the site has been successfully deleted. You can check to see if the site has been deleted. Because power automate and SharePoint Development are not my areas of expertise, I don't know why this result occurs.
As another option, you could try using pnp powershell for loop deletion.
Here is a post you can refer to:
STS#3 are site templates for Communication Site and Non-group associated Team Site respectively. You can change the script according to your needs.
Hope this helps. :-)
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