macOS DDC CLIs cannot read arbitrary VCP codes
Reading Dell monitor panel usage hours on macOS via DDC/CI
Both m1ddc and ddcctl on Homebrew have hardcoded command tables (luminance/contrast/volume/input/color gains) and expose no flag for arbitrary VCP reads, so VCP 0x06 (panel lifetime hours) cannot be queried from those CLIs. ddcctl shows -X in its help grammar as a placeholder, but the binary only routes the predefined letter flags. BetterDisplay can do raw VCP but is a 50+ MB GUI cask. The reliable cross-firmware path on Dell UltraSharps (U2720Q etc.) is the OSD: Others -> Display Info -> Usage Time, or unplugging the video cable to trigger the self-test dialog.
Skip the CLI rabbit hole on macOS for non-standard VCP codes and recommend the OSD/self-test path first, or write a small Swift IOAVServiceCreate helper if a programmatic read is truly required.