There is a binary file name called pyThrobber and it is available and not final like pxthrobber. What is the use of this? I have customize that rule but it doesn't reflect in my busy indicator. What is the use of that one???? I am using 8.3 Cloud version.
The pxThrobber contains the gif of 7.x version busy indicator. In 8.x versions, the busy indicator is not configured using binary files instead they are achieved through CSS implementation. In 8.x versions, CSS spinner is used.
You can override the CSS spinner by overriding the pega.ui.busyIndicator.prototype.createIndicatorImage function. You can try adding the CSS in your custom harness or you can override in the user work form.
Please have a look at the below articles which may help you :