I can’t connect to Bluetooth

Have you already seen these support guides?:--> Pair a third-party Bluetooth accessory with your iPhone, iPad, or iPod touch - Apple Support

and/or:--> If you can't connect a Bluetooth accessory to your iPhone, iPad, or iPod touch - Apple Support

If you get no help, you can contact Apple Support using this link:--> Contact – Official Apple Support

or

Make an appointment at an Apple Store or Authorized Service Provider and have your device inspected: Apple – Location Selector

Regards

Giulio

What, exactly, are you trying to connect to.

You can not pair it with a computer or another mobile phone. That's not a feature of the iPhone.

The accessory you're trying to connect to must be in discoverable (pairing) mode in order to pair with it.