Connect Audio Prompts very robotic on iOS 18.5 - Why?

Hi All

I have an Edge 840 Solar with OS 27.14 and iPhone 12 Pro with iOS 18.5, both set to English

I have enabled the Audio Prompts for the Edge 840

When speaking the data (heartrate, speed etc.) the spoken voice on the iPhone (or connected Bluetooth earpieces) is a very robotic, unusual, non-Siri voice.

Changing voices in Settings > Accessibility > Spoken Content has no impact on the Garmin Connect spoken voice.

When testing the voice in Garmin Connect using the Alert Volume setting, you hear a standard male Siri voice.

But when the activity voice prompts occur, the voice used is totally different - a very robotic, unusual, non-Siri voice.

Can anyone prompt me to a specific setting or settings to make the Audio Prompts more natural?