I wonder, where IPB4 have the sitemap.xml file generated, so I can serve it for google? I find only sitemap.php

You just submit sitemap.php in Google Search Console, this includes all XML files.

Edited March 16, 20223 yr by Sonya*

Sitemaps are automatically submitted to Google when they're generated/updated. 

However, if you want it to be viewable in Google Search Console you still need to submit it for it to show up in the UI. <community_url>/sitemap.php is the correct URL to submit