ios screen off without lock

With the iPad's auto-lock function set to Never, unless you have an iPad Pro with FaceID and its Attention Awareness feature enabled, the iPad's screen will remain switched-on until the iPad's battery is exhausted.

As such, if you wish your iPad screen to automatically sleep, you must enable the auto-lock feature.

Go to Settings/Display & Brightness, tap Auto-Lock, and tap Never.

Never, if that’s what you set. If you have Attention Aware features on the screen will dim if you aren’t looking at it.