My Ubuntu version is 20.04. My notebook is connected a monitor with HDMI(multiple monitors).

I've connected my Bluetooth speaker, because my monitor sound is not good, and I tried to change Output Device to my Bluetooth speaker.

sound settings

But it doesn't work. I still get the sound from the monitor. Even if I change the output device to something else, the sounds keeps coming out of my monitor.

When I disconnect HDMI, it works well.

What thing I have to check?