fix internet connection on my iphone 13pro

If WhatsApp is working then your iPhone is connected to the Internet.

Regardless, I would try the following, in order. Stop if a particular step resolves the issue:

• Restart your iPhone - Apple Support
• Force restart iPhone - Apple Support
• Toggle Airplane Mode OFF, then ON.
• Reset your iPhone's Wi-Fi settings: Settings > General > Reset > Reset Network Settings
  • This resets Wi-Fi networks and passwords, cellular settings, trust settings, and VPN and APN settings that you’ve used before.
• Perform a "Reset All Settings" reset: Settings > General > Reset > Reset All Settings

... and what have you tried, so far yourself, to resolve this so that we don't offer potential solutions that may not have already worked for you?