Hi
Apple Watch Series 3 supports compatible Bluetooth 4.2 devices and is also backward compatible with Bluetooth 4.1 devices.
Apple Watch Series 3 - Technical Specifications
In order to be able to listen to music from your Apple Watch, compatible Bluetooth headphones or a Bluetooth speaker are required, paired directly to the watch:
- Listen to music on your Apple Watch - Apple Support
- Connect Bluetooth headphones or speakers
- Use Bluetooth accessories with Apple Watch - Apple Support
Note that Apple Watch does not support using Bluetooth headphones for making or receiving phone calls.
Apple does not publish a list of compatible headphones.
Most - but not all - Bluetooth headphones that use the A2DP Bluetooth profile can be used with Apple Watch for listening to music that has been synced to your Apple Watch.
Headphones that are least likely to be compatible are those that also offer additional built-in functions such as fitness tracking, a heart rate monitor and/or a a built-in media player.
For any such headphones, I suggest that you check with the manufacturer whether they can be used with Apple Watch.