Not so. Gzip’s window is very small - 32K in the original gzip iirc, which meant even identical copies of a 33KB file would bot help each other. Iirc it was

Not so. Gzip’s window is very small - 32K in the original gzip iirc, which meant even identical copies of a 33KB file would bot help each other. Iirc it was Bzip2 that bumped that up to 1MB, and there are now compressors with larger windows - but files have also grown, it’s not a solved problem for compression utilities. It is solved for backup - but, reatic, and a few others will do that across a backup set with no “window size” limit. …. And all of that is only true for lossless, which does not include images or video.