Only certain Roku models support Bluetooth devices.
How to use Bluetooth headphones for Headphone Mode on your Roku streaming device | Official Roku Sup...
I have a Dell monitor that may be similar to yours. The 12V port is to power the Dell speaker that can be attached to the monitor. The speaker gets the audio by connecting to the computer.
You'll need a Roku device that supports a Bluetooth speaker or an HDMI audio extractor that you can connect to a speaker.
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