There is a work around for creating "real" docx footnotes from html using LibreOffice. LibreOffice is able to turn links into footnotes if they are properly defined/formatted in the html file.
For instance, importing an html file with this code into LibreOffice
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8"/>
<title>Footnote Test</title>
<meta name="generator" content="LibreOffice 7.5.9.2 (Windows)"/>
<style type="text/css">
@page { size: 21cm 29.7cm; margin: 2cm }
p { line-height: 115%; margin-bottom: 0.25cm; background: transparent }
p.sdfootnote { font-size: 10pt; line-height: 100%; margin-left: 0.6cm; text-indent: -0.6cm; margin-bottom: 0cm; background: transparent }
a.sdfootnoteanc { font-size: 57% }
</style>
</head>
<body lang="en-US" link="#000080" vlink="#800000" dir="ltr">
<p align="center" style="line-height: 100%; margin-top: 0.42cm; margin-bottom: 0.21cm; page-break-after: avoid"><font face="Liberation Sans, sans-serif"><font size="6" style="font-size: 28pt"><b>Footnote Test</b></font></font></p>
<p style="line-height: 100%; margin-bottom: 0cm"><br/></p>
<p style="line-height: 100%; margin-bottom: 0cm">This is a text followed by a footnote.<a class="sdfootnoteanc" name="sdfootnote1anc" href="#sdfootnote1sym"><sup>1</sup></a></p>
<div id="sdfootnote1">
<p class="sdfootnote"><a class="sdfootnotesym" name="sdfootnote1sym" href="#sdfootnote1anc">1</a>This is a footnote text.</p>
</div>
</body>
</html>
results in "true" footnotes in LibreOffice. This document can then be saved as docx.
I did it once used this formatting with over 100 footnotes and it worked perfectly.