After months of frustration, I've just found such a simple solution that hopefully it will help lots of other people.
If your iPhone is already Bluetooth connected to your headphones or speakers, go into Settings on your iPhone, and turn off Bluetooth.
Then on your MacBook, go into System Preferences, and click Bluetooth.
Then in your MacBook, turn Bluetooth off, then turn Bluetooth on.
Your Bluetooth speaker should then automatically turn up in your MacBook's list of Devices.
Then in your MacBook's Bluetooth, click the speaker's icon within the list of Devices, so that the speaker's icon turns dark blue.
Thanks to BusinessInsider.com for giving me the clue:
"Make sure your devices aren't already synced: If your Bluetooth headphones aren't connecting to your Mac, it may be because the headphones are already paired to another device, like your iPhone."
You can easily connect your headphones to a Mac from System Preferences, Control Center, or the Menu Bar.
www.businessinsider.com
This unbelievably simple solution worked for me.
Let me know if it works for you
Best,
LR