macbook pro bluetooth link to external speaker

You do not paint a very big picture...You do not say what exact Mac /model /year /size /retina /touchbar is this 

or

what exact macOS you are currently running? 

or brand name, product you are having issues with; new problem old problem, what changed?

—hold the shift option keys and click open the BT icon>Reset

Bluetooth - Apple Support

Connect a Bluetooth device with your Mac - Apple Support

Using a Bluetooth mouse, keyboard, or trackpad with ... - Apple Support

Pair a third-party Bluetooth accessory with your ... - Apple Support

Resolve Wi-Fi and Bluetooth issues caused by ... - Apple Support

Apple USB-C Charge Cable Replacement Program - Apple Support

https://www.apple.com/support/usbc-chargecable/

Well to add to your reading:

Using USB devices with your Mac - Apple Support

https://support.apple.com/en-us/HT201163

also, any of these items may be involved:

• Power Adapter cable recall

Apple USB-C Charge Cable Replacement Program - Apple Support

https://support.apple.com/exchange_repair

• firmware update for the Apple Multi-Port display adapters (specifically to reduce interference).

About the USB-C Multiport Adapter Update 1.0 - Apple Support

• LG-display recall -- to address Wi-Fi interference so severe, it knocks the Router off the air if too near the Router.

https://9to5mac.com/2017/02/03/lg-fixes-wifi-interference-problems-with-ultrafin e-usb-c-5k-display-new-units-unaffected/

Some USB 3 devices can generate radio frequency interference that can cause Wi-Fi and Bluetooth devices operating in the 2.4GHz band to have issues communicating with your computer. 

Here are some general tips in an effort to resolve your issue:

If your using USB device(s) have a cable long enough that you can move the device, place it away from your Mac—and make sure not to place it behind your Mac, or near the hinge of its display. The antennas for Wi-Fi and Bluetooth are located there, and USB 3 devices placed there might interfere with your wireless connections.

If you're using adapters or dongles on a Mac computer with Thunderbolt 3 (USB-C) ports, plug them into the front port on the left side of your Mac, or into the ports on the right side (if your computer has them). These ports are the farthest away from the antennas, making interference less likely.

To avoid interference on the 2.4GHz band using Wi-Fi, try using the 5GHz band instead. You can change this on your wireless base station. Bluetooth always uses 2.4GHz, so this alternative isn't available for Bluetooth.