Hi, @Sharon. About this:
If you were using Netlify as the hosting for the apex domain then, yes (but you won’t be so you can’t).
If the apex domain hosting is at the WP host (SiteGround), that hosting is handling the HTTP request and they would need to proxy to Netlify in some way. Note: we strongly recommend against proxying to Netlify. Proxying from Netlify to other hosting is fine but we do not recommend proxying to us.
If you use the subdomain method (instead of the “sub-path” method), Netlify hosts the subdomain directly and there is no proxying involved.
I want to mention, you can stop search engines from indexing certain sites or pages so SEO won’t be impacted:
If you don’t want the test sites indexed, please use one of those methods to prevent it and no SEO impact will occur. Alternatively, you can also enable site-wide password protection on the test sites so SEO isn’t affected but this feature is only available on Pro plan teams or above.