Idea is used by JetBrains (as to my understanding) and, as to my understanding, may in certain setups create cache directories. That's no good, these should be ignored.
Since a long time, developers have been able to use Visual Studio Code inside of Unity. I don't claim exactly to know how it works, but regardless its cache directory should be ignored, whether it is ever created or not (if not now, it might be in the future).