It happened sometime today. There is lots of chatter on a similar problem, except that usually the greyed out files and folders won't open. I did restarts and quit and restart with no change. When I did Cmd. + Opt + dot, everything disappeared— with repeat they came back. Tried making aliases an new folders, and copy and paste. This seemed to work, but is a short time they grey returned. I reinstalled Mojave on my iMac, but still the desktop f & F in the finder window were greyed out. My IMac has been working well lately. I guess I can still work with the greyed f & F, but I am a little uneasy that this might be a precursor to a larger problem. Has anyone else experienced this and found a solution?