Because these units are often generic, there isn't one single official website. You have two main options:
No. This is a hardware limitation. The Mediatek AC8257 chipset (which runs the YT9216) has drivers locked to Android 8.1 (Go edition) or, with heavy modding, Android 10 (Go). Many "Android 12" labels on eBay are simply build.prop forgery. The most stable V001 update you can install is the November 2023 Patch Level modded ROM based on Android 10. android yt9216bj-00012-v001 update
Note: If you cannot find a download link, check the stickers on the metal casing of the head unit (you may need to unscrew it from the dashboard). Look for a date code or a specific website URL printed on the PCB board. Because these units are often generic, there isn't