https://www.youtube.com/watch?v=2k8x8V77CrU

you don't need muti-activities , it's muti-tasks

android:documentLaunchMode

https://mouzishuo.github.io/2018/11/16/android:documentLaunchMode%E5%B1%9E%E6%80%A7%E7%9A%84%E4%BD%9C%E7%94%A8/