Using delimiter $$ on its own line no longer works in MathJAX 3.x with Blogger

Question

I've previously used MathJax 2.x on Google's Blogger platform, inserting the library and configuration references in the site's template HTML, as per many recommendations here and elsewhere.

On a new Blogger blog, I decided to use MathJAX 3, using the call that always pulls in the latest 3.x version.

In both cases I use dollar symbols, $ and $$, to trigger inline and display maths.

With MathJax 3.x, I can no longer use $$ on it's own line. The following doesn't work.

$$
x=y
$$ 

I need to do this:

$$ x = y $$

The first is cleaner, especially for multiline equations.

Anyone know how to make this work with MathJAX 3.x?

Here is my config code:

<script>
    MathJax = {
      tex: {
        inlineMath: [[&#39;$&#39;, &#39;$&#39;]],
        displayMath: [[&#39;$$&#39;,&#39;$$&#39;]]
      },
      svg: {
        fontCache: &#39;global&#39;
      },
      options: {
        enableMenu: false
      }
    };
    </script>
    <script async='async' id='MathJax-script' src='https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml.js'/>

I'm not an expert so there may be something wrong with this. I have spent several hours reading the MathJAX documentation for 3.x and 2.x.

The problems remains if I use the default delimiter characters, so is not related to the $ symbol.

I have tried the config to replace HTML tags with TEX to try to replace the generated

with nothing, but that fails with an error.