It is pretty common on many laptops that the bios no longer has an option to disable the internal Bluetooth.
If it’s not possible to disable BT in your laptop’s bios there are other methods to accomplish this. The easiest method is to write a udev rule.
You should hopefully be able to disable your internal bluetooth device with a udev rule.
Create a udev rule with the proper name (in the required location), with the following command:
sudo touch /etc/udev/rules.d/81-bluetooth-hci.rules
Open the newly created /etc/udev/rules.d/81-bluetooth-hci.rules file with your favorite text editor.
In your text editor, paste the contents of the line below into the udev rule:
SUBSYSTEM=="usb", ATTRS{idVendor}=="0bda", ATTRS{idProduct}=="b721", ATTR{authorized}="0"
Save the changes and exit the text editor, and then reboot.
Hope that helps if your bios cannot disable your internal Bluetooth.