This is really very bad news since our app needs it and it worked with iOS 15 and now isn't working with iOS 16 anymore. So with the update users are loosing functionality. Sad that Apple users have less and worse possibilities in this case compared to users of all other platforms.
klues
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Additionally it's not the case what you've described as the expected behaviour: e.g. the Spanish voice "Jorge" is preinstalalled, but also not listed via the Web Speech API.
With iOS things again became worse. In iOS 17 there was at least access to some high quality voices in webapps, which now are gone again. Please change this back, it's really affecting the user experience for your users in many modern webapps, where it's a real disadvantage to have an iOS device compared to Android. This is really a point why I'm recommending people to not buy Apple devices in my daily life (especially for people who are needing the speech features, where I have many contacts).