About the XML Sitemap Generator
The XML Sitemap Generator turns a plain URL list into a valid sitemap.xml — optional lastmod (today), changefreq and priority attributes included. Validate the deployed file with the Sitemap Checker.
Google largely ignores both; lastmod is the one hint that carries weight when it is accurate.
50,000 URLs or 50 MB uncompressed — beyond that, split into multiple files with a sitemap index.