Pandoc man page says:

Thus, the following yields a list with numbers followed by a single parenthesis,

          9)  Ninth
         10)  Tenth
         11)  Eleventh

Sorry, there is no single parenthesis:

$ for i in 1 2 3; do echo $i\) $i; done
1) 1
2) 2
3) 3
$ for i in 1 2 3; do echo $i\) $i; done | pandoc
<ol type="1">
<li>1</li>
<li>2</li>
<li>3</li>
</ol>

No I didn't forget to turn on an extension. Same problem as 1) for (1).

Anyway you'll need pretty fancy HTML5 to get those parenthesis rendered, so maybe on the man page mention the parenthesis don't work in HTML output mode.

$ pandoc --version
pandoc 3.1.11.1