JBL CHARGE 3 connect to Mac / Macbook (solution)
I've seen a bunch of messages over the last few years about an inability the use a JBL speaker with a Mac. The problem seems to be with the JBL's ability to pair with multiple Bluetooth devices at the same time. In my case, I had my iPhone and Macbook connected to the speaker. It worked fine with the phone, but it wouldn't show up in the list of audio devices on the Macbook even though it paired successfully.
Once I turned off Bluetooth on the phone, the speaker showed up in the Macbook's audio device list, and I could use it for playback. So it looks like macOS is not handling that situation correctly.
I wouldn't be surprised if this happened with other Bluetooth speakers with similar functionality, but at least there's a workaround.
