Hello vittorio_27,
Based on what you've shared with us, it looks like you may have an app on your iPhone that's installed a root certificate. You can learn how to resolve this issue by following the steps here: How to delete an app that has a configuration profile on your iPhone, iPad, or iPod touch - Apple Support
You may find these steps helpful:
Delete the app and its configuration profile
To delete an app and its configuration profile, follow these steps.
1. Delete the app
* Touch and hold the app until it jiggles.
* Then tap the delete button
in the upper-left corner of the app to delete it. If you see a message that says, "Deleting this app will also delete its data," tap Delete.
2. If the app has a configuration profile, delete it.
* Go to Settings > General > Profiles or Profiles & Device Management,* then tap the app’s configuration profile.
* Then tap Delete Profile. If asked, enter your device passcode, then tap Delete.
3. Restart your iPhone, iPad, or iPod touch.
Thanks.