Visual Studio Code - is there a #Compare feature like that plugin for Notepad ++? - Stack Overflow
Here is my favorite way, which I think is a little less tedious than the “Select for Compare, then Compare With...” steps.
1) Open the starting file
2) Open the Command Palette (F1 or Ctrl + Shift + P)
3) Type Compare Active File and select Compare Active File With...
4) Select the new file to compare with. You can either select a recent file from the dropdown list, or click any file in the Explorer panel.
Note: This works with any arbitrary files, even ones that are not in the project dir. You can even just create 2 new Untitled files and copy/paste text in there too.