How to get unknown style rule in MS Edge with JavaScript

I want to use object-fit CSS rule.
This is not supported in MSIE and MS Edge Browser.
While there are some polyfills for IE, there is none to my knowledge that works in Edge.

E.g. the polyfill fitie by Jonathan Neal works with IE, but not in Edge (at least not on my machine). This is because fitie uses element.currentStyle and element.runtimeStyle which are MS only JS objects which do not any support in Edge browsers anymore. But if I use window.getComputedStyle(element).getPropertyValue('object-fit'), Edge returns nothing.

So how do I obtain the value of CSS rule object-fit rule with JavaScript in MS Edge browser?

img = document.getElementById('i');
s = self.getComputedStyle(img);
console.log('object-fit: ', s.getPropertyValue('object-fit'));
console.log('-ms-object-fit: ', s.getPropertyValue('-ms-object-fit'));

div {
  width: 400px;
  height: 320px;
  overflow: hidden;
}
#i {
  display: block;
  width: 100%;
  height: 100%;
  -ms-object-fit: cover;
  object-fit: cover;
}

div {
  box-sizing: border-box;
  border: 1px solid gold;
}
div,
p {
  font-family: sans-serif;
  font-size: 20px;
  width: 400px;
  margin: 0 auto;
}

<p>img: Has object-fit CSS rule, but does not appear in MS Edge JavaScript log</p>
<div>
<img src="https://dummyimage.com/640x240/333/444.png" id="i" />
</div>

Edit

It must be possible somehow, as it is not fully ignored.
The Developer Tools show the rule curly underlined

Bonus question:

Is there any polyfill for object-fit that works in Edge?