SharePoint content embedded in Confluence: Not affected. After a Confluence Cloud site subdomain rename (for example from abc.atlassian.net to xyz.atlassian.net), the macros keep rendering correctly, and no configuration is needed. For the rename steps, see Atlassian's guide on updating a product URL.
Confluence pages embedded in SharePoint: May need attention. The Confluence Page web part stores the page's URL, and SharePoint's HTML Field Security allows a specific Confluence domain. After a subdomain rename, update the allowed domain (and, if needed, re-copy the embed script) so that the embedded pages continue to work.
This is different from using a custom domain such as confluence.company.com, which this does not cover.