Hello, I have RTL8821AE, and according to my tests, the device functions perfectly without "rtl_bt/rtl8821a_config.bin" firmware. So I believe trying to symlink different firmware to this file for the sake of just bypassing the error message alone can be unnecessary and harmful.
It appears that this specific firmware isn't provided by the manufacturer and is missing in the latest Linux kernel at the time of writing (please check: https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/rtl_bt). For anyone getting other missing firmware errors regarding the RTL8821AE device, like "rtl_bt/rtl8821a_fw.bin", please install the "firmware-realtek" package (make sure to add "non-free" component to your sources list to make this available). Some Debian desktop installations seem to misconfigure PulseAudio, which may result in failing to negotiate connection with Bluetooth speakers/headphones even when your Bluetooth adapter is fully functional. The symptom of this problem is usually a "Connection Failed: Protocol not available" message. To work around this problem, make sure "pulseaudio-module-bluetooth" is installed, then run the following: pactl load-module module-bluetooth-discover Best regards, Vladislav