It looks like this is broken in iOS 17.2.1. WKWebView that plays HTML element works. But if the app is in the background or if the screen is locked, you cannot start playing a new audio element.
You'll receive a .ended event from the ended audio file. You can use that to set the .src to a new audio file. You can call .play() on it, but no audio will be heard.
This is happening even if Info.plist has Required background modes including "App processes data in the background" and "App plays audio or streams audio/video using Airplay".