How I Fixed The Modern Warfare Copying Add-On Glitch! (2020) Read The DESCRIPTION! 

For the record, this was just another method that could work just in case you cleaned your disk and it still wouldn’t copy/download-which happened to me. Thank You!
Just to summarize what I said in this video:
-Grab (a different) MW disk & put it in your PS4
OR
-Exchange your disk at the store and put that disk in your PS4
Or-Thanks To The Comments:
Try to clean your disk😂