H3 / Android 9 (P or Pie): multi display OK, but multi input?

Hello Community 
First message, will try to follow the rules Slight smile

Reading this https://community.renesas.com/automotive/r-car-h3-m3-cockpit/f/cockpit-f/17652/android-9-or-android-10-with-dual-multi-display-display-support-som

I'm happy to run the H3 with 2 dislplays, and able to start an activity via adb on the second display.
But I didn't find anyway to get a working mouse (or any other input) on the second display.
Seems that even google doesn't support this in AOSP 9: https://source.android.com/docs/core/display/multi_display/input-routing

Obviously I have to keep Android 9 (else  would switch to 10 :) )

Any solution ? Feedback?
Many thanks