Relevant to lobste.rs because the author specifically shows how Asciidoctor is suitable for code-heavy presentations.
I can’t propose enough Reveal-md. Like you, I searched for years for a good tool for my random presentations.
Reveal.js looks amazing, people ALWAYS ask me in what tool I do presentations. With markdown as editing language you can really create slides very fast and yet have all expressibility of HTML if needed. You can also give to people plain markdown code of the presentation so they can open it in an editor of their choice, like vscode.
For PDF export I have custom shell script that runs all via pandoc to export it. But I prefer to give people HTML export so that it is exactly the same as I present it. This doesn’t require server to start, just load index.html and follow along.
Marp can also export PDF if you don’t want to code. It looks like they further develop it here
== EDIT ==
PDF export is now available within reveal-md. See here
Nice! I find this pretty compelling. I’m a big Markdown fan/user/proponent/maintainer, but Asciidoc looks more and more like it shines when things start to get more complicated.
Agree! A great bonus is that, when things are simple, AsciiDoctor looks mostly like just markdown. My only complaint is that for reference links the reference needs to come before, and not after, as in markdown.
Amusingly, even though I’ve used Markdown way more than AsciiDoc, I never get Markdown’s link format right the first time. Link first or text? Which part goes in  and which goes in ()? AsciiDoc’s link:target[Text] is more memorable to me because it’s a macro the same as include: or image:.
I keep all my documents in asciidoc and my hugo blog is all asciidoc. I really prefer the format over markdown.
Quick comparison if you are interested: https://asciidoctor.org/docs/asciidoc-vs-markdown/
Asciidoctor is amazing amd is also rendered by GitHub. The only caveat is that GitHub doesn’t render file includes, most likely to avoid file traversal attacks. This is true for all of the formats that I have tried.