Why is my MacBook Pro screen so dark on full brightness?

Your screen isn't defective, and it isn't really at full brightness. On a MacBook Pro 14"/16", the top of the menu slider is the everyday cap macOS sets, not your panel's real limit. The system holds half the range in reserve for HDR. Your screen tops out near 500 nits, while the display itself can hit about 1,600. First rule out the usual dimmers in System Settings: auto-brightness, True Tone, and Low Power Mode. If it's still too dark outside, MacBrightness opens that reserved range on the same brightness keys, system-wide. The free Splitscreen Mode lets you see the brighter screen before paying the $5 one-time.