Realtek RTL8761B is a USB Bluetooth 5.0 dongle made by Realtek. It is identified by lsusb as
0bda:8771 Realtek Semiconductor Corp.
The dongle has been supported by the
CONFIG_BT_RTL since Linux 5.8. The driver requires firmware. The firmware has been available in the linux-formware package since April 2020.
You will need to upgrade your kernel to 5.8+ if you have an older kernel and you want to use this donge.