Secondary users are Android users with separate apps and data saved between sessions
Also, I tested the app myself on an Android emulator running Android API Level 34 and I was not able to read the internal data of other users. However, I wasn't even able to locate the contents of the guest user using the device explorer at all - I guess it's not mounted or not visible, if someone knows more about this, feel free to tell me how to find it.
There isn't a lot of documentation available but according to https://developer.android.com/work/dpc/dedicated-devices/multiple-users:
Also, I tested the app myself on an Android emulator running Android API Level 34 and I was not able to read the internal data of other users. However, I wasn't even able to locate the contents of the guest user using the device explorer at all - I guess it's not mounted or not visible, if someone knows more about this, feel free to tell me how to find it.