I will try this out, thanks!

Any idea if playlists can directly work in external but non Jellyfin apps like finamp or kodi with Jellyfin for kodi? If not can playlists be saved/exported for use in those contexts?

Theoretically possible but someone would have to reverse engineer the protocol and write a new service that works based on that

There are some projects but all that I’ve seen are open source head units that either: are terrible and aren’t android auto/carplay (eg they only have the most basic of integration, can show notifications and play music via Bluetooth) or they emulate android auto/carplay without the necessary licensing/hardware (so you still ultimately rely on google/apple)