My iPhone WiFi is greyed out

Is Bluetooth greyed out also? If so that is almost certainly a hardware problem with the radio chip that supports both Wi-Fi and Bluetooth. Contact Apple support→https://getsupport.apple.com.

You can try these troubleshooting steps, but no guarantees:

• Go to Settings/General/Transfer or Reset Phone/Reset/Reset Network Settings
• If that doesn’t resolve the problem, back up your phone and restore to factory settings and test

1. How to back up your iPhone, iPad, and iPod touch - Apple Support
2. Restore your iPhone, iPad, or iPod to factory settings - Apple Support - follow the instructions to restore using your computer, do not using Settings/General/Reset (which is not included in those instructions) TEST AGAIN
3. If that fixes it, Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

None of that work

What was the result when you contacted Apple Support?

https://getsupport.apple.com