Insert following tekst (blue marked) inside your theme header.php
<head>
<meta charset="<?php bloginfo( 'charset' ); ?>">
<link rel="profile" href="http://gmpg.org/xfn/11">
<link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>">
<?php wp_head();
remove_filter ('the_content', 'wptexturize');
remove_filter ('comment_text', 'wptexturize');
remove_filter ('single_post_title', 'wptexturize');
remove_filter ('the_title', 'wptexturize');
remove_filter ('the_excerpt', 'wptexturize');
?>
</head>
https://wordpress.org/support/topic/removing-emdash-replacement
Example old situation when copying tekst from the website (look at the quote marks):
New situation:
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