Wanted - Device that does Bluetooth audio RX and automatic line level switching

[Psi]

Has anyone seen anything for sale that is a BT audio receiver and automatic line level switch vs passthrough?
ie, you pass a line level signal through the device and if the BT is connected (and playing audio) then the BT sound is routed to the output, and if not connected or no sound then it routes the input to the output instead.

I want to add BT audio to my android car stereo which has no working AUX.
The car stereo has its own BT but it doesnt work and is not fixable (software bug or complex hardware bug).
I don't really want to replace the stereo because it's tied into CAN bus and fully setup for the car with steering wheel controls etc...
I don't care about voice calling/microphone, just want to listen to music playing on phone.

I currently have some cable and a DTDT switch hacked into the audio line signal going to the SIP stereo amp chip inside, with a headphone plug on the end to connect to the phone. However my new phone has no audio jack and BT is easier anyway. So I want to add BT audio to it and have it automatically switch between BT and passthrough.

I could design a PCB with BT rx module, analog switch and ADC/MCU to do this myself.  But just wondering if anyone has seen anything off-the-shelf that can do this.
Happy to pay $100 for it if it works.

[themadhippy]

youtuber mend it mark has featured something that sounds like its wot your after, unfortunately his web site https://perton-electronics.co.uk/products.html  dont give much info on it but might be worth giving him a shout