Unable to remove unknown Samsung S23 Bluetooth device

No it just means the device was added with an app that is on your phone. Go to Settings > Privacy & Security > Bluetooth, and one of the apps listed there is the reason and turning off access for that app will remove the device.

Once you have identified the app using that method, the device can also be removed from the app. One example based on your other devices is an external bluetooth speaker where in the app for that speaker you have allowed the S23 phone to control or play music to the device.

That is a BLE device (Bluetooth Low Energy). BLE devices connect to a specific app on your iPhone, rather than to the iPhone itself. That might be a data transfer app for a Samsung smartphone.