I used a sitemap generator gem, it created a sitemap.xml.gz (after I installed the gem and ran the ruby script)
I added this file to google search console, but it doesn’t like it. It says, your Sitemap appears to be an HTML page. Please use a supported sitemap format instead.
Perhaps this issue might better be brought to the gem, they might have an idea? Or perhaps a site such as StackOverflow might be better place to get answers to debugging questions such as these? Good luck finding your answer!