if I understand correctly there is no way to make FOSS AA (protocol itself is not open unless reverse engineered). There needs to be separate implementation like AA / CarPlay and headunit needs to support it. Current best case scenario is miracast supporting headunits (but this is one directional)

since this is F-Droid community I didn’t mention it, but I’m looking for FOSS solutions. My phone is degoogled and doesn’t have android auto