You can use the template_include
hook to accomplish this.
Add this to your active theme’s functions.php
file (or create a plugin).
add_filter( 'template_include', 'wpse376643_load_html_page' );
function wpse376643_load_html_page( $template ) {
if ( is_page( 'the-page' ) ) {
// You'll have to use the server path to your index.html file.
$template="/path/to/your/content/oct2020/index.html";
}
return $template;
}