Since HTML5 specifies how to handle all parse errors, and the handling of an XML self-closing tag is to ignore it unless it's part of an unquoted attribute value, it's valid HTML5.
Decades later, I'm still mildly annoyed when I see self-closing tags in HTML. When you're not trying to build a strict XML document, they're no longer required. Now I read them as a vestigial reminder of the strict XHTML dream.
EDIT: I just checked, and my site (at least the index page) still validates! https://validator.nu/?showsource=yes&doc=https%3A%2F%2Fander...
EDIT2: Hey, look, if you still want to use self-closing tags where they're not required: go nuts! I'm just explaining why I don't use them anymore.
About page here: https://anderegg.ca/about/
And the feed is here: https://anderegg.ca/feed.xml
I had a lot of fun with this emulator on Archive.org, and included some quick notes about using it with macOS: https://archive.org/details/canoncat
Can mods change the linked article away from the thin blog post?