please note last code is best so far , only that it does not accept speaker as an argument

app.py

@@ -24,8 +24,7 @@ def set_model(model_name_str):
     tts = TTS(model_path)
     speakers = tts.get_speakers()
     value = speakers[-1]
-    speaker.choices = speakers
-    speaker.value = value
+    return speakers, value
 
 def main():
     logging.basicConfig(level=logging.INFO)
@@ -65,6 +64,15 @@ def main():
         layout="rows",
         debug=True
     )
+
+    # Set the speakers dropdown choices and value based on the selected model
+    speakers, default_speaker = set_model(model_name_dropdown.value)
+    speaker.choices = speakers
+    speaker.value = default_speaker
+
+    # Update the speakers dropdown when a new model is selected
+    model_name_dropdown.set_action(set_model)
+
     iface.launch()