Disconnect Bluetooth device named Plateau PR1 from my iPhone

• Are you talking in your Bluetooth Settings or something else?
• Is it under My Devices showing as Connected?
• Is it missing the info button next to it under My Devices? That indicates an App is using the Bluetooth device and you can remove Bluetooth access for the app at Settings > Privacy & Security > Bluetooth.

A screenshot of what you are seeing may be helpful. If what you are seeing is actually "Platco PR1", that is usually a device having to do with automation such as a remote, tv, or home automation. There is likely an app associated with that device where it can be removed. Removing the app or revoking bluetooth permission using the above steps will also remove the device from your Bluetooth Settings.

• Since you have the Info button listed, are you able to Forget the Device there.
• And what do you have listed at Settings > Privacy & Security > Bluetooth?
• And also at Settings > Bluetooth? I would guess it is also listed there and important to see if the Info button is included to indicate a paired device that can be removed by tapping Forget this Device, or if no info button indicating that an app has been given permission to add/remove a bluetooth device.

The Platco PR1 is an interface used by many devices and the identifier is not helpful in knowing which device that is, but finding the app that uses Bluetooth in the location above is usually helpful to narrow it down. Switch off an app until you see the one that removed the device. Once you identified the app, then you have more options such as removing the app or removing the device from the app.