WiFi Auto-Join option turned on itself

If your iPhone is automatically connecting to a saved WiFi network without your manual selection, and the "Auto-Join" option is turning itself on, there could be a few possible explanations for this behavior. Here are some things you can check and do to troubleshoot the issue:

1. Location-based Auto-Join: iPhones have a feature called "Auto-Join Hotspot" that allows the device to automatically join known WiFi networks based on your location. It uses cell tower and GPS information to determine your location and connect to familiar WiFi networks. To check if this feature is enabled, go to Settings > WiFi and scroll down to find the "Auto-Join Hotspot" option. You can disable this feature if you don't want your iPhone to automatically connect to known networks based on location.
   1. The pic below says: Known networks will be joined automatically. If no known networks are available, you will be notified of available networks.
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2. iCloud Keychain Sync: If you have multiple Apple devices (e.g., iPhone, iPad, Mac) and use iCloud Keychain to sync your WiFi network settings across devices (Refer to the third Screenshot below), changes made on one device can propagate to others. So, if you accidentally enabled the "Auto-Join" option on one device, it might get synced to your iPhone as well. To avoid this, ensure that you manually manage WiFi networks on each device separately.
   1. See the pic below: Which says, Your device and other devices using iCloud Keychain will no longer join this Wi-Fi network If Forget is tapped.
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