Should you edit photos or video at max brightness on a Mac?

For color-critical editing, no. Calibrate to a fixed reference level instead, because max brightness skews how you read exposure and color. SDR photo work is usually done around 120-160 nits in a dim room. The Pro Display XDR also ships with reference modes like Photography P3-D65 and Design and Print P3-D50. They lock white point, gamma, and brightness for exactly this reason. Crank past those and you'll edit shadows and saturation to compensate for a too-bright screen. Seeing the screen outdoors is a separate need: more brightness genuinely helps you read it on a sunny patio. MacBrightness opens the reserved range on a Pro 14"/16" or XDR for visibility; it's not a calibration tool.