Redirecting subdomain to root domain with same name

I am looking to redirect my subdomain, to, but it says that "/subdomain is already a page for this project. I think it’s doing this because both the subdomain and the root domain have the same name.

Aside from this issue, will be a Substack page with a custom domain, not a Webflow page.

I have two questions:

First, how can I do this without Webflow thinking it’s the same page?

Second, is this a bad idea from a Google rank perspective? I want Google to know that both pages (Webflow and Substack) are related to one another.

Any help would be greatly appreciated!

Here is my site Read-Only: LINK
(how to share your site Read-Only link)