Why is DDC disabled for my Apple Cinema Display when another app can use it?

BetterDisplay treats Apple displays differently and can deliberately withhold DDC control on Apple displays to avoid brightness problems. DDC may work in another app but still cause problems after sleep or wake.

The relevant override is Settings > Displays > [display] > Device Control > Device Control Settings… > Treat as generic third-party (non-Apple) display. It appears for displays identified as Apple-made or otherwise Apple-capable. Enabling it allows the display to be handled as a generic device so DDC can be configured.

The app warns that this can cause permanent issues on some older Apple displays. Keep the default unless you have established that your particular display and connection can safely use DDC. Check sleep and wake as well as brightness changes. An affected display can wake black or stop responding.

This override is not a general fix for DDC through docks, and it is not expected to appear for an ordinary third-party monitor. See DDC through adapters and docks and Device Control Settings for the separate connection and controller choices.