Can't get value of property in SVG on web page in JS

[deniznet]

Hi!
I make diagram in web-version draw.io. I add properties for rect (by right click), for example (mydata="something"), and save to SVG.
Next, I add this SVG on web page (Next.JS client component) and add listening events - onMouseClick in JS. I get element by click (event.target) - this is my rect. But it has not element mydata. Why?

"use client";

export default function Roadmapper({ svg }: { svg: string }) {
  const handleClick = (event: React.MouseEvent<HTMLDivElement>) => {
    console.log(event.target);
  };

  return (
    <>
      <div
        style={{ width: "100%", height: "100%" }}
        onClick={handleClick}
        dangerouslySetInnerHTML={{ __html: svg }}
      />
    </>
  );
}

How to set my data for element in draw.io to get it in web-page in JS?

in console I get:

<rect x="0" y="80" width="120" height="60" rx="9" ry="9" fill="url(#drawio-svg-VJUeQuwQImHvvxXrS3Zj-gradient-light-dark_fff2cc_281d00_-1-light-dark_ff9933_a95100_-1-s-0)" stroke="#d6b656" pointer-events="all" style="fill: url(&quot;#drawio-svg-VJUeQuwQImHvvxXrS3Zj-gradient-light-dark_fff2cc_281d00_-1-light-dark_ff9933_a95100_-1-s-0&quot;); stroke: light-dark(rgb(214, 182, 86), rgb(109, 81, 0));"></rect>

Thank you!