Update microcode: microcodeIntel not working

I get the kernel warning “[Firmware Bug]: TSC_DEADLINE disabled due to Errata; please update microcode to version: 0x22 (or later)”.

I have enabled microcodeIntel in environment.systemPackages = with pkgs; [ microcodeIntel ]; and did nixos-rebuild switch, but the warning is still there.

NixOS 20.09.2497.4a75ca4a4e7, Kernel: x86_64 Linux 5.4.86, Processor: i7-4770K

What else can I do?

In order to get the microcode updates, you should enable this option:

hardware.cpu.intel.updateMicrocode = true;

Adding microcodeIntel to packages is not necessary.