How to fix StandBy mode not working on iPhone with iOS 18.4 ?

Be aware that Standby Mode will only show a continuous display if the iPhone supports "always on display". Here is list of iPhone models that support this feature:

• iPhone 14 Pro
• iPhone 14 Pro Max
• iPhone 15 Pro
• iPhone 15 Pro Max
• iPhone 16 Pro
• iPhone 16 Pro Max

The tags appended to your post suggest that you have an iPhone 13. While this model has an OLED display, it does not support "always on" in Standby Mode. As such, in Standby Mode, the screen will always switch-off after a few seconds - but can be woken for few seconds with simple tap.

The iPhone User Guide provides more information:

Keep the iPhone display on longer - Apple Support

Having just tested Standby Mode with an iPhone 13 Pro, this mode works as expected.

Try a forced restart of your iPhone - as this will often clear an isolated or post-update software issue:

Force restart iPhone - Apple Support

13userfr wrote:

It’s not works at all.

You could take the device in to a Genius Bar, get the battery changed, and also tell them about the StandBy Mode. They could run diagnostics, etc. to try and find out what’s going on. That way you’d kill two birds with one stone.

• Genius Bar Reservations: Genius Bar Reservation and Apple Support Options
• Locate Apple Stores & AASP’s: Find a Reseller 
• iPhone Service & Repair: iPhone Repair and Service - Apple Support

What do you mean by "reload" or "force reload?" Do you mean "restart?"

Are these the instructions you followed?

Force restart iPhone - Apple Support

What you you mean when you say you tried "differenty types of charging?"

Be aware that Standby Mode, whether or not your iPhone has an "always on" OLED display, will only work while:

• the iPhone is in Landscape screen orientation
• is inclined at 45-90° (i.e. not laying on a flat surface)
• is connected to a source of external power (either via its charging port or MagSafe/Qi inductive charger)
• is locked

13userfr wrote:

and also I have 77 battery and there’s message in settings that I need to change the battery.It can be cuz of that?

Hello!

Let us get a clear picture of your problem. You put the device on its side while charging, correct? It has to be upright and on its side.

Your battery is significantly degraded, and it would be a good idea to replace it, however I can’t see why that would stop StandBy Mode from working.

Do you expect the screen to remain on and not turn off? Or does StandBy Mode not turn on at all?