2018 A5 B9 v Galaxy S10 Lite

I've had my phone bluetoothed to the car for some time now but just noticed when the phone rings it doesn't use the the car system. I found my way to the "Ringtones" page and it says "Your device does not support this facility". The ringtone, MOON, is shaded out as is the option to change ringtone volume. It worked perfectly well before Christmas. I can still make / receive calls, texts directory etc.
No big issue but seems a bit odd.