I've recently proceeded with setting up new Xiaomi device and used Mi Mover to try to copy from older Xiaomi device. The app said "copying apps, some apps it cannot copy but e.g. Telegram, WhatsApp were ticked as to be copied". After completion app asked to rate it.
I wanted to check results before rating and only media from WhatsApp, telegram were copied. Why can't app of phone manufacturer take care of installing apps on new phone and transfer all user data? I guess Xiaomi can provide its' app with root privileges etc. I have not been able to find answer via googling.