Hi Metzger,

To access the core options you need to enable it on the retroarch.cfg file, under the retropie 2.3 image this can be found here:

/opt/retropie/configs/all/retroarch.cfg

The lines you need to change are: (Thanks Trimmtrab)

input_enable_hotkey_btn =
input_menu_toggle_btn =

The “input_menu_toggle_btn =” is your button joypad number

You will also find there a commented line

# Toggles Menu
# input_menu_toggle = f1

Uncomment this one too.

Please remember:
These are the paths for the 2.3 image, the old image has different paths

For this to work make sure you are using the latest image 2.3
https://www.petrockblock.com/retropie/retropie-downloads/

Please let us know if this has helped you.