I hate to link this but uh can’t find a better resource with quick Google
https://www.reddit.com/r/ChineseLanguage/wiki/faq
Essentially you’ll want to decide to go with Simplified or Traditional mandarin, Pinyin vs Zhuyin. Taiwan and HK use Traditional, you’ll learn through Zhuyin, while China/SG/MY (and many others) use Simplified, learnt through Pinyin. Ignore dialects eg. Cantonese, Hokkien all that for now.
Probably not specific to Pixel, but on several occasions I noticed when I set a destination in my P6, then connect that to my Android Auto - I have to do that again