It's used a lot in the publishing industry, which stores the content in JATS and other similar XML markup. It's also used by the US government for bills, etc.

Typically, these use XSLT on the backend to transform the content to HTML to be sent to the web browser.

And there's RSS which was mentioned in the previous discussions. Podcasts will typically have HTML renderings of that data, but if you opened the RSS in a web browser you could use XSLT to provide a user-friendly view of the content.

XSLT can also be used to provide fallback rendering for unsupported content, such as converting MathML to HTML for browsers without support. -- Chrome as of 109 supports MathML Core, but doesn't support the content markup (used for more semantic markup of common constructs like N-ary sum, integrals, etc.), so would still need something like XSLT to convert that markup to the presentation markup supported by Chrome.