Google's John Mueller was asked on Twitter if the sitemap ping tool still works or not. John said that he is "not aware of any changes there, and the URL seems to be responding to get requests as usual." In fact, the official documentation still has this as an option.
The docs say "Use the ping tool. Send a GET request in your browser or the command line to this address, specifying the full URL of the sitemap. Be sure that the sitemap file is accessible."
The format to ping Google is https://www.google.com/ping?sitemap=FULL_URL_OF_SITEMAP
Of course, just because you ping Google with new URLs, it does not mean Google will index all of the pages and show all the pages in Google Search. John added on Twitter "a sitemap ping doesn't guarantee crawling though."
I'm not aware of any changes there, and the URL seems to be responding to get requests as usual. A sitemap ping doesn't guarantee crawling though.
— 🧀 John 🧀 (@JohnMu) September 12, 2021
Forum discussion at Twitter.