You can keep your site hidden from search engines before launch and still have sitemaps you can verify. Hide the site with a single WordPress-level switch instead of robots settings in Rank Math.
- In Rank Math, go to Titles & Meta → Global Meta and set the global robots option to index (remove noindex and nofollow).
- Clear any per-page noindex robots meta that was applied to individual pages during development.
- Keep the site hidden with Settings → Reading → Discourage search engines from indexing this site. This setting keeps a site-wide noindex tag on every page until you turn it off.
- Flush permalinks and clear the Rank Math sitemap cache plus any object cache.
- Reload sitemap_index.xml and open each sub-sitemap.
At go-live, turn off Discourage search engines from indexing this site. That one setting is what should be turned off at launch.