A1450 appears to be a Lightning to 30 Pin Adapter – with a Lightning plug on one end, and a socket for the old 30-pin dock connector on the other. A 30-pin dock connector was a feature of many early iPods, iPhones, and iPads – but I believe Apple switched over to Lightning completely by some time in 2012.
The iPhone X has a Lightning socket, so it sounds like you are telling us that your Mercedes car speakers have a 30-pin dock connector plug that goes into the 30-pin dock connector socket.
Is that correct? If so …
I see some USB-C to 30-pin dock connector (socket) adapters on Amazon. One of them might be a plug-and-play replacement for the A1450 cable. Another possibility might be to get an Apple USB-C to Lightning adapter, and to daisy-chain the two Apple adapters (thereby creating a "USB-C to 30-pin adapter").
If your car stereo has a USB-A or USB-C input, you might want to forget about the old 30-pin dock connector and use a USB-C to {USB-A, USB-C} cable that supports data transfer.