JavaScript blocks display of the other side of card

The problem here is mainly document.write(), which clears the document on first write as far as I understand from Document.write() - Web APIs | MDN

Try this front template:

<div id="front"></div>

var list = "{{Eng}}".replace("<br>", "\n");
var word = list.match(/.*/);
var front = document.getElementById("front");
front.innerHTML = `Eng: ${word}<br>Rus?`;

You also have to use var instead of let or you will get errors because Anki uses the same webview for front and back templates and only recycles it periodically.