Not sure why you mentioned this. At least on Arc, or any distro based on it like Artix, the ucode per CPU is offered as a separate package:

% pacman -Ss ucode
system/amd-ucode 20241111.b5885ec5-1
    Microcode update image for AMD CPUs
world/intel-ucode 20241112-1 [installed]
    Microcode update files for Intel CPUs
world/iucode-tool 2.3.1-5
    Tool to manipulate Intel
galaxy/amd-ucode-xz 20230625.ee91452d-4
    Microcode update image for AMD CPUs
extra/intel-ucode 20241112-1 [installed]
    Microcode update files for Intel CPUs
extra/iucode-tool 2.3.1-5
    Tool to manipulate Intel

If your distro doesn't help with ucode packages, you can ultimately download it from intel/amd/whatever. And the same applies for the hardware firmware in general.

So it's true that some hardware won't properly work out of the box by using libre-linux, but nothing prevents you from getting the required firmware from other packages or sources. Granted that doesn't make things easier. And granted that might defeat the purpose of using linux-libre, but you might at least only add only strictly required binary blobs for your current hardware.