If you have Screen Time turned on on your iPhone or iPad, you may not be able to change some settings thus the Set Automatically option will be dimmed, or grayed out. ... To disable it, go to Settings > Screen Time and scroll down and tap the red “Turn Off Screen Time” button.

Why can't I toggle off set automatically in date and time?

About privacy and Location Services in iOS 8 and later -- Tap Settings > Privacy > Location Services > System Services (at the bottom of the list), and make sure that "Setting Time Zone" is turned on. See if you're able to turn "Set Automatically" off under Settings > General > Date & Time now.

Why is set automatically grayed out in iPhone Date & time settings?

If the device has a Screen Time passcode, then the option to turn on Set Automatically will be dimmed, or grayed out. If the time on your device is wrong after you sync it with your computer, your computer's time might be wrong. ... You might want to select "Set date and time automatically."