I have a Safari extension that plays audio via the javascript AudioContext API. It was working fine under iOS 17 and is now broken under iOS 18. It does not play audio at all.
I've tried in both the iOS 18 public beta and the iOS 18.1 developer beta. It is broken in both of them.
I've also created Feedback item FB15170620 which has a url attached to a page I created which demonstrates the issue.