Welcome to Apple Support Communities! There's an article that goes over what to do if the setting to turn on Wi-Fi on your iPhone appears "grayed out" or dim. Here are the steps it recommends:
Follow these steps to resolve the issue:
- Verify that airplane mode is off by tapping Settings > Airplane Mode.
- Reset the network settings by tapping Settings > General > Reset > Reset Network Settings.
Note: This will reset all network settings, including Bluetooth pairing records, Wi-Fi passwords, VPN, and APN settings
- Ensure that your device is using the latest software. To do so, connect your device to your computer and check for updates in iTunes.
- If your issue is still unresolved, perform a software restore in iTunes.
Have a good one,