There is a bug in macOS 14.0 that sometimes prevent disk images from loading if they have a license agreement attached to them.
This bug has been fixed in macOS 14.1, so if you can, please update to macOS 14.1.
If you must stay on macOS 14.0 do the following to allow the disk image to load:
In terminal execute the following command:
xattr -d com.apple.quarantine <path_to_disk_image>
Be sure to replace <path_to_disk_image> with the path to the disk image.
If you just downloaded Iris into your Download folder, you can copy and paste this command into Terminal:
xattr -d com.apple.quarantine ~/Downloads/Iris_*.dmg