Hey @Adie_Stevson,
I saw this on GitHub:
The thinking being that if it is some focus stealing script on a remote page that you can’t control, the browser won’t focus a hidden element. And there’s a good likelihood that your onload will fire after their focus changing script.
Also suggesting there:
<iframe style="display: none;" onload="this.style.display='block';" href="..."></iframe>
Or
<iframe style="position: absolute; top: -9999em; visibility: hidden;" onload="this.style.position='static'; this.style.visibility='visible';" href="..."></iframe>