Hi - Your previous thread pretty much says the same - it would be better to keep the converstaion there. Incidentally is this also your thread at iodé? If not it might have something of use (although result seems to have been failure for that person if it’s not you).
The problem may partly be Ford’s Sync3 if that’s a proprietary system/protocol - it will rely on phones having certain capabilities and USB functions. So to eliminate that - if you haven’t done this already - do you know someone with a stock Android Phone (i.e. a Samsung or Pixel or similar, that’s off the shelf and not degoogled) you can plug into your vehicle and test - does it work fine? Because if it doesn’t then you know no Android is ever going to work the way you want. If it does work then you know it’s just settings or a OS software issue (no support for something).
I would strongly suggest, if you haven’t already, you do the above - because otherwise you don’t even know for sure what you want to do would ever actually work on your vehicle with a modern Android handset?
As an aside, It’s also possible for Ford Sync3 to connect to a phone over USB even at a basic level (no Car Play or Android Auto) for the functionality it claims, it’s relying on certain privacy invasive apps (or settings or functions) on the phone - and they just won’t be present on iodéOS because the whole point is to remove those.
Automobile systems are one of the worst sources of privacy breaches and have zero security so I can’t imagine there would be anything in a degoogled OS that would willing support connection without going through Car Play or Android Auto…