Unknown Bluetooth device “S10” on my iPhone

There are S10 headphones, earphones, an AirPlay device, and an Android Galaxy S10 phone. Undoubtedly others.

Alternatively, the (free) LightBlue app on iPhone or iPad can be useful for identifying local Bluetooth activity,

Does it have an i next to it? If it does, tap on the i and see what it is.

Is it under Other Devices? If so, it is a nearby device; Bluetooth displays all devices in range, as it doesn’t know whether they are yours or not; you should ignore it.

Is it under My Devices with your others, but no i? In that case it is a BLE device that connects to an app on your phone, but does not have to be paired. This could be a medical or other device that communicates only with its matching app.