Hi Bizmuth,
Thank you for using the Apple Support Communities! If you're experiencing an issue specifically when connected to Wi-Fi, we would recommend the steps in the following article that may help, testing after each step:
If your iPhone, iPad or iPod touch won't connect to a Wi-Fi network
Additionally, if you're using any security or VPN software, test by temporarily uninstalling the software (not just disable), restart your device, then test again.
We would also suggest the guidance in the following resources that can also help:
Recommended settings for Wi-Fi routers and access points
Resolve Wi-Fi and Bluetooth issues caused by wireless interference
Hope this helps!
Have a great day.