Cast

sudo dmidecode -t 2

sudo lspci|grep VGA
 VGA compatible controller: NVIDIA Corporation GP108 [GeForce GT 1030] (rev a1)

I plugged in a tp-link UB500 Plus usb dongle, to pair with Office Popsicle (an Echo Pop).

Honestly I plugged it in and the bluetooth icon appeared, nice.

Make sure service is running.

sudo systemctl start bluetooth # to start it
sudo systemctl enable bluetooth # to run on next reboot

This will let you do "bluetooth things"...

bluetoothctl

But honestly I can't say what worked to connect cast to office-popsicle. I just kept banging on it on both sides until it was connected.