ow is the background in the main menu? Is that also very dark?

no the menu screens that form a band down the middel of the game window from setup are fine I tried it with the HDR on in your setup as it selected it as the default I tried full screen and Windowed with no major change I was tring with firstt HDR set to max gama in your setup then with it off and brightness and contrast at max

Double check that HDR is disabled: hold the Cmd button on game startup to get to the configuration menu, if it is not coming up automatically (which should be the case, with an option to turn off).

From a quick search it looks like the Radeon R9 M290X does have some HDR support, though, so as long you are also outputting to a display that has HDR support, this may be an issue with the settings.

The version of the game I have is via the Apple App Store
Version 3.6.69.4648

The Basic HDR resolutions as well as the defauls from the display
2560X1440 is the default
I normaly run at 2048x1142 but 1600x900 is anothe basic selectio
2860X1620 and 3200X1800 going in the other direction but text is to hart to read up there so 2048X1142 is my normal
Higher res is posable i understand by messing about in the terminal comands but I dont do that sort of thing much any more
the actual specs are
AMD Radeon R9 M295X:

Chipset Model: AMD Radeon R9 M295X
Type: GPU
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 4 GB
Vendor: AMD (0x1002)
Device ID: 0x6938
Revision ID: 0x0000
ROM Revision: 113-C773AA-731
VBIOS Version: 113-C773A1-014
EFI Driver Version: 01.00.731
Metal: Supported, feature set macOS GPUFamily2 v1
Displays:
iMac:
Display Type: Built-In Retina LCD
Resolution: 5120 x 2880 Retina
Framebuffer Depth: 30-Bit Color (ARGB2101010)
Main Display: Yes
Mirror: Off
Online: Yes
Automatically Adjust Brightness: No
Connection Type: Internal



I will give this instrustion a try at 2048x1142 thanks
and report back

To calibration HDR, if you have not already done so:
- Ensure you have Automatic Brightness Adjustments enabled (System Preferences/Display)
- Go to Options->HDR settings
- Start with Max Brightness and Min Contrast
- Press ‘Apply’
- DON’T apply general video settings. Just click close button and Discard the settings; there is a known bug with this
- next, adjust the HDR Brightness/Contrast settings to your preference


Try creating a new user account, switch to that account and try starting the game from there, from the app container (in /Applications).

Try doing a clean boot and test the game. Start/restart your Mac and hold the Shift key down as soon as the progress bar comes up in the startup window, releasing it after the desktop appears. Alternately, from the login window, hold the Shift key when you click the Log In button, and release it when you see the Dock