I had the same question and found a workaround. This ADO help page mentions "Only Markdown headings are considered for TOC (HTML heading tags aren't considered)."
For example, to eliminate the duplicate page title in the embedded TOC, I used <h1>page title</h1>
instead of #page title
. This eliminated the page title from the embedded TOC, but the page title still rendered in the same visual style on the wiki page. The same approach worked for subtitles: using <h3>subtitle</h3>
instead of ###subtitle
rendered the subtitle appearing like a subtitle in the wiki page, but kept it out of the TOC.
It's a manual approach but it helped keep the TOC simplified which is what I wanted.