Hey,
I have the Problem that the Sound for my bluetooth Headset under Linux, doesn’t work correctly. I had this Problem already and changed the driver that I use for my bluetooth dongle, after I did that, the Sound worked without any Problems, after I’ve updated the System the Sound Problems are back. My Bluetooth Dongle needs the rtl8761b drivers and these are the drivers that 've installed on my NixOS too, here is the snippet from my configuration.nix
boot.blacklistedKernelModules = ["rtl8xxxu"];
boot.extraModulePackages = with config.boot.kernelPackages; [pkgs.rtl8761b-firmware];
And this is the output from lsmod | grep rtl
btrtl 28672 1 btusb
bluetooth 913408 36 btrtl,btmtk,btintel,btbcm,bnep,btusb,rfcomm
firmware_class 49152 10 r8169,btrtl,snd_hda_intel,xhci_pci_renesas,btmtk,nvidia,btintel,btbcm,btusb,drm