After update, background turned black, the dock is missing
On rare occasions, I have had to go nuclear and clean out specific preference files:

rm ~/Library/Preferences/com.apple.finder.plist

One might argue that you should back it up first. In that light, I suggest simply moving it out of the way and force-quitting Finder.

cd ~/Library/Preferences
mv com.apple.finder.plist com.apple.finder.plist-orig