To proactively check for and apply an update for Citrix Workspace:
To update without using the automatic updater, download and run (as Administrator) the latest installer from Citrix. This would be necessary if Citrix Workspace automatically prompts to update but then fails with this error hidden behind the progress dialog--in this screenshot I've moved it out from behind:
Could not load file or assembly 'Newtonsoft.Json, Version=12.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
The Citrix article about this says that doing this will allow it to resume automatically updating successfully in the future.