Here’s an updated version I was able fix!
<script type="text/discourse-plugin" version="0.8">
api.onPageChange((url, title) => {
$("img").on("contextmenu", function(e) {
e.preventDefault();
});
});
</script>
<script type="text/discourse-plugin" version="0.8">
api.onPageChange((url, title) => {
$("body").on("contextmenu", ".cooked img, .mfp-img", function(e) {
e.preventDefault();
});
});
</script>