In macOS Font Book, there's a smart collection for Monospaced (Fixed Width) fonts.

I've tried to look into how this is determined, and I'm not sure. FontForge docs seems to say that it (FF) should decide for itself when the font is monospaced, although it also mentions some (OS/2?) setting for this, and I don't know if this would have an impact.

tl;dr it would be nice if Monocraft was automatically added to the Fixed Width smart collection in Font Book, and I'm not sure why it doesn't show up there.