@aeva
The official stance is that they are evil, evil binary blobs. But you can use https://gitlab.com/nonguix/nonguix to get them and other naughty proprietary software as long as you don't mention it in official channels.
Edit: I didn't find a more approachable package listing, but you flip through https://gitlab.com/nonguix/nonguix/-/tree/master/nongnu/packages if you're looking for something specific other than microcode.