Always on display

Always On is more like “usually on” or “always on except…"

Here's the Apple support article→Use Always-On display with your iPhone 14 Pro or iPhone 14 Pro Max

Always-On display goes dark when you don't need it

To save battery life, the display is completely dark when:

• Your iPhone is lying face down 
• Your iPhone is in your pocket or bag
• Sleep Focus is on
• Low Power Mode is on
• Your iPhone is connected to CarPlay
• You're using Continuity Camera
• You haven't used your iPhone for a while (your iPhone learns your activity patterns and turns the display off and on accordingly, including if you set up an alarm or sleep schedule)
• Your iPhone detects that you moved away from it with a paired Apple Watch (Always-On display will turn on when your Apple Watch is close to your iPhone again)

If you have Sleep Focus activated, you may also experience that the Always On screen goes black.

You can disable Sleep Focus in the Control Center. Tap the Focus button and disable Sleep Focus.

Also check if you have activated Low Power Mode If so, you can disable Low Power Mode here:

Settings → Battery → disable Low Power Mode