nx-btred is a Bluetooth audio driver/redirector for Switch.
It uses the audrec:u service to record game audio, and then outputs it on the new audio bluetooth driver introduced in firmware version 12.0.0.
⚠️ Warning ⚠️
YOU USE THIS AT YOUR OWN RISK. Not every headphone brand has been tested. There may be really loud noise. Be careful, start out with a low volume, and then increase, if you like. In case of any type of malfunction, the sound will stop immediately if you hit the power button.
Install firmware 12.0.0+.
Install latest Atmosphere.
Install latest MissionControl.
Download nx-btred and unzip to your SD card.
Enter the homebrew menu.
Launch the btpair application.
Press X to scan.
Select your headphones and click A.
Wait for it to pair.
Due to a limitation of the audrec:u service, only games audio can be recorded (not the system applets).
Thanks to ndeadly, SciresM, yellows8 and the rest of the Switchbrew crowd.