To start Apple Diagnostics on a Mac, shut it down, then press the power button and immediately hold Command-D until diagnostics begin (progress bar appears). This works on Intel and Apple silicon Macs (post-startup options on silicon).

Option A: Option-D starts Internet Diagnostics (older Macs), not standard Diagnostics.

Option B: Command-Option-D isn’t a valid combo.

Option D: Shift-D isn’t used.