I asked about the arb because I'm an owner of Mi note 3 and soon an android 9 will be released. Also I saw on telegram post that Xiaomi released Pie for MI MIX 2. After several comments they noted that arb is active but nowhere on miui forum they mentioned it. That's why I wanted to check the...
Use Winrar to extract the contents of the fastboot rom - there should be several files and folders including flash all bat after decompression. Also rename the downloaded file to something shorter before unzipping it.
Download Aida64 from Google paly store and in System section it will show the codename of the device you own.
The accessories should fit - check gsmarena for the exact dimensions of the two models but I think they are the same.