I have now already started 3 times. Either the installation aborts or when it is supposed to be finished, the VM boots, but it does not reach the login window, a black window remains.
I followed the instructions, but I have to set the RAM memory to 4GB, because a RAM-disk is created when booting from the ISO image.
Just now the installation window has disappeared again, but if you look at /mnt in the BSD System Monitor, you can see that this partition is getting more and more occupied. But I don't notice when it is finished.

I use ufs instead of zfs to save resources.

What are the best settings in VirtualBox in detail?

I have been installing FreeBSD 12 VM for quite some time now and have also provided it with a MATE desktop. This VM runs on this computer without problems.

https://wiki.ghostbsd.org/index.php/Installation_Guide

MacBook Pro late 2008
CPU: Intel(R) Core(TM)2 Duo CPU P8600 @ 2.40GHz
RAM 8GB
HD SSD 960GB
Mac OS X - ElCapitan 10.11.6
VirtualBox 6.1.16 r140961 (Qt5.6.3)

Greetings
Fritz

The recommended ram for the new iso is 6GB under that we can't say it will be stable.

In my mac I have only 8GB RAM, my FreeBSD 12 installation with MATE works well with 2 GB RAM.
Whats the differences between FreeBSD 12 with MATE (self configured) and GhostBSD?

Or is ZFS from the ISO image this problem?

It is a live system using ram for running ZFS for the live filesystem to make it RW filesystem. It will get tweaks in the future. But for now, it is what it is.

From my collection of GhostBSD screenshots and recordings at https://photos.app.goo.gl/cwEjGheYMSPmo77f9

• https://photos.app.goo.gl/tWMPSgCU9c7suWp6A was an example of GhostBSD-21.04.27.iso with a black screen (not presenting the desktop environment) with less than 6 GB.

ACPI shutdown succeeded.

A later boot with 4 GB was fine.

BSDonMac wrote: ↑Thu Dec 03, 2020 10:22 am In my mac I have only 8GB RAM,

1. Give 6 GB (or as much as you can) to the guest
2. boot from GhostBSD-21.04.27.iso
3. install
4. shut down
5. remove the .iso from the guest
6. set the guest to 4 GB or less
7. boot.

my FreeBSD 12 installation with MATE works well with 2 GB RAM. …

With a slightly earlier installation (from pre-release GhostBSD-21.04.26.iso) I test-drove with less than 4 GB. The host was FreeBSD 14.0-CURRENT on a circa 2013 HP EliteBook 8570p with 16 GB real memory, and USB flash drives as ZFS caches (one for the internal hard disk drive, another for the external hard disk drive where I store my VirtualBox data).

I can't predict how well your old Mac will perform for combined use of the two operating systems.

How much graphics memory?

APFS or HFS Plus? No APFS with Mac OS X 10.11.6.

What's the model identifier?

Mac Specs By Machine Model/Model ID - Macs By Identifier: EveryMac.com

BSDonMac wrote: ↑Thu Dec 03, 2020 10:08 am … I use ufs instead of zfs to save resources.

For your use case, OpenZFS should be fine. Go with it, try it.

What are the best settings in VirtualBox in detail? …

Without going into detail: use VBoxSVGA (not VMSVGA).