Someone sent me a link about XSLT getting deprecated. And, that’s expected. Welcome to the real world? Browser APIs are not as reliable as you’d think.
In fact, one can sus out the “true” APIs of anything by analyzing a company’s repositories for usages (Mozilla, Google, Apple). This allows you to guess at deprecations, wrongly.
I’m not an XML person, but if XSL transformations are interesting (like to Markdown), look at Paligo/xee (Rust). I think I wrote about extensible stylesheets (and Saxonica) somewhere after being impressed by XML pros in action.