On the Z Fold 3, when the phone is locked and the screen is off, opening the phone up shows the lock screen on the main display. Even if the phone is set to the lowest brightness setting, the lock screen will always be much brighter, almost full brightness. Once it's unlocked, the screen dims back down to the brightness it was set to.
This seems like an odd behavior, and can at times be almost blinding. The lock screen should just match whatever brightness the phone is set to.