I edited your post to mark the <br> so it won’t be invisible anymore. When you post example Markdown, HTML, or other code, please mark it as code to prevent the forum software from rendering or garbling it. Thanks!
The lack of support for Markdown inside HTML blocks is unfortunately an intentional deviation from the CommonMark specification that Obsidian’s Markdown derives from.
The example you posted doesn’t actually work in Reading View, tho it looks like it does. If you open the developer tools and inspect those elements, you’ll see it produces an empty div with the margin style, followed by the list, followed by an empty div with no style.
