After six months of work I'm delighted to tag the first stable release of the 4.x branch of the (Not-so-) Simple XML Sitemap module.
The project is in a really good place right now. At the moment of writing, drupal.org reports it being actively used on around 90k of Drupal 8/9 websites while having 0 open bug reports. This either means you people are lousy bug reporters, or we are doing a descent job at responding. :)