With the upgrade to macOS 10.14.1 my OneDrive for Business finder integration went AWOL. Getting it back was pretty easy, but getting the instructions in one place was a little trickier. This may also work for other file sync/share tools like Dropbox or Resilio Sync, but I know it works for OneDrive.
Step One is to open the System Preferences > Extensions > Finder Extensions screen.
Toggle the checkbox next to “OneDrive Finder Integration” making sure that when you’re finished it’s checked. Next, Option-Click the Finder icon in your dock and select Relaunch.