notification sound works on phone only, not in Android Auto

When incoming mail arrives I get a notification sound on the phone which is fine. But when I'm connected to Android Auto the notification sound doesn't play through either the phone or the car speakers. Other apps such as Signal and WhatsApp play the notifications in Android Auto. Only Thunderbird doesn't. How can I make Thunderbird play the notification the same way it does when not connected to Android Auto. Nothing seems to be blocked in the notification settings for Thunderbird. The phone is a Pixel 10 Pro BTW. Thank you.