I have an Aluratek ABC53F device that I use to play music on my stereo via Bluetooth. I can connect to the device just fine from my phone, but not from my laptop, a Dell XPS L322X running Ubuntu 18.04. Note that the laptop Bluetooth is not completely dysfunctional. For instance, I can pair my laptop with my phone and transfer files.
There are plenty of similar questions on the internet (e.g. Bluetooth Broadcom 43142 isn't working), but as far as I can tell, none of the solutions proposed there worked for me. In particular, I have already tried upgrading BlueZ to version 5.50.