If you're unable to sign out of your Apple ID on your iPhone, it may be because restrictions are enabled. To fix this, follow these steps:
1. Open the Settings app on your iPhone.
2. Tap on "Screen Time."
3. Scroll down and select "Content & Privacy Restrictions."
4. Enter your Screen Time passcode if prompted.
5. Toggle off the restrictions by tapping on the switch next to "Content & Privacy Restrictions."
Once you've turned off the restrictions, you should be able to sign out of your Apple ID without any issues. Remember to input your Screen Time passcode when prompted.