The Message and MessageQueue calls are related to DoEvents and Msgbox. They are indeed based on reflection but they do work on Android P.
I'm using an Android P device for several months now. I don't think that this report is accurate.
If you call Msbox on an Android P device then you will see these messages in the unfiltered logs:
Accessing hidden method Landroid/os/MessageQueue;->next()Landroid/os/Message; (light greylist, reflection)
Accessing hidden field Landroid/os/Message;->when:J (light greylist, reflection)
Accessing hidden field Landroid/os/Message;->flags:I (light greylist, reflection)
Accessing hidden method Landroid/os/Message;->recycleUnchecked()V (light greylist, reflection)
light greylist methods will work properly:
https://developer.android.com/preview/restrictions-non-sdk-interfaces
With that said, you should avoid using modal dialogs or calling DoEvents:
DoEvents deprecated and async dialogs
I think that the other methods from this report are also considered light greylist. The best option is to test it on an Android P device.