Very nice add-on! Thank you! :)
To make it mostly work in Godot 4, you have to load it and "Convert Full Project"
Then remove (or correct - even though I'm not sure how) the last line of Code in the Example Scene "$VoiceGeneratorAudioStreamPlayer.stream.audio_stream = load("res://addons/" + item)" And add the Sound, in the Inspector of the AudioStreamPlayer by clicking Randomizer, to the Streams tab.
This then only allows the one sound that's in the inspector to play but but other than that the Voice generator works great.
The Animation shouldn't be to hard to fix - I just didn't bother since I didn't need it for my project. :)