install/55478: netbsd 9.0 - Installer freezes on macbook pro late 2013

[marko.bauhardt%mailbox.org@localhost]

>Number:         55478
>Category:       install
>Synopsis:       netbsd 9.0 - Installer freezes on macbook pro late 2013
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jul 10 13:35:01 +0000 2020
>Originator:     Marko Bauhardt
>Release:        9.0
>Organization:
>Environment:
MacBook Pro late 2013 Retina
>Description:
I try to install NetBsd on my Macbook Pro late 2013.
I'm using a USB stick.
The installer starts correctly, so I'm able to choose between 2 options
1) Install NetBSD
2) Drop to Boot prompt

I chosed 1)
After a few seconds the display is getting more light/brighter. (I don't know how to explain). And then the display switched to black color, and I can do nothing. No sysinst blue screen is visible.

Btw
at the moment there is a FreeBSD installed on that machine.

Any hint how to get more verbosity about what exactly happens.

Thx 
Marko
>How-To-Repeat:
Boot release 9.0  from USB stick.
>Fix: