Today (Oct 5) Liopold Novelli and I will give a presentation at DrupalCon Europe 2021 entitled XML-sitemap optimizations for large sites: a case study.
In this study, we outline steps we have taken to both increase the crawl rate and efficiency of the sitemap for a relatively large website.
The solution centers around the simple_sitemap_extensions module. It is a drupal contrib module, initially developed by Mathias Müller. Lio and I continued it. The presentation is the first part of a case study that Lio and I are conducting.