Some of my coworkers subscribe to my site's feeds using Microsoft Outlook. Outlook doesn't support XHTML feed contents, but it does support escaped HTML feed contents. My Atom feeds use XHTML but my RSS feeds use HTML, so I re-introduced RSS discovery for them.

Also, Outlook renders feed contents using the same HTML renderer it uses for emails. That HTML renderer is the Microsoft Word HTML renderer. Word's HTML renderer is based on Internet Explorer's MSHTML (Trident).
So IE was sunset on consumer editions of Windows two days ago, but I guess it lives on like this. I updated my my thoughts on IE's not-quite-demise to reflect that: https://seirdy.one/notes/2022/06/15/internet-explorer-is-almost-gone/