[Does NOT work with Trisquel 10 upgraded to Linux 5.4.0-150-generic] ASUS USB-BT500 Bluetooth 5.0 Adapter. (Possibly) uses Realtek rtl8761bu Bluetooth controller. A Comfast chip with identical controller is used in testing, and is recognized by Trisquel 10. HOWEVER, from the Bluetooth panel, no devices can be found despite my phone can find a bunch of devices around. [Edited]

By checking files and documentation shipped along side (Realtek's) driver provided by ASUS, we can find firmware file of rtl8761bu inside the rtkbt-firmware folder.

The original information posted here was wrong, after research we can find ASUS BT-500 Bluetooth dongles are using a rtl8761bu controller rather than some Broadcom one. Information about the chipset inside this product is nowhere to be found on the Internet. Yet I find the firmware for rtl8761bu among the folders, so that chip is probably the one inside this BT-500 model. I'm going to buy one dongle with same controller to prove this. Feel free to correct me if I am wrong.

PS: Simple devices like Wi-Fi/Bluetooth dongles will usually work with free software as long as it's main chip (SoC) is supported by the driver. Occationally the driver will work for similar chips.

PSS: On Github/Gitlab and many other coding platform, you can find many third-party drivers for popular chips. Many are blobless, especially those without a firmware directory and doesn't contain files like *.cab. (*.bin files are too ambiguous to determined directly)

PPSS: The scan issue's cause has been found, it's an unpatched bug. See:https://askubuntu.com/questions/1370663/bluetooth-scan-doesnt-detect-any-device-on-ubuntu-21-10