Welcome to the community!
This is an interesting question so I ran it by the tech team and we decided to do a test for you just to be 100% sure.
Our QA just created two test projects for a domain and subdomain similar to yours and as soon as the data loads, I’ll let get back to you with the results.
Thanks for your question!
we tested this and you indeed need only 1 project for both domain and subdomain.