In the original posts, I explained that Squarespace have prevented clicking on nav folders in 7.1 which is why previously-posted solutions don't work.
The solution below, posted by @tuanphan should work when added to Settings > Advanced > Code Injection. Modify the links (/folder1, /page1 and so on) to suit your folder urls and pages.
<script src="https://code.jquery.com/jquery-3.5.1.min.js" integrity="sha256-9/aliU8dGd2tb6OSsuzixeV4y/faTqgFtohetphbbj0=" crossorigin="anonymous"></script>
<script>
$(document).ready(function() {
$('a.header-nav-folder-title[href="/folder1"]').click(function() {
window.location = "/page1";
});
$('a.header-nav-folder-title[href="/folder2"]').click(function() {
window.location = "/page2";
});
});
</script>
Note that it may appear to give strange results whilst logged on (for example a double refresh within the preview window) but this is due to the way that preview window is framed, but it should work fine for website visitors (or whilst logged out).