It is not possible to exclude a page from the automatically generated sitemap. CMS Collection pages with no content in them will not be included in sitemaps by default.
If you prefer to write your own custom sitemap.xml, you can and add that to your Webflow project.
- Disable the auto-generated sitemap by switching the Auto-generate sitemap toggle to "No"
- Paste your custom sitemap.xml in the text area
- Save and publish