Packaging files into an archive
The selected files are written into a standard ZIP container in the order you added them, keeping their original names and contents. The archive opens in Windows Explorer, macOS Finder, and any archive utility.
Why the archive is not much smaller
JPG, PNG, WebP and AVIF files are already compressed, so squeezing them again saves almost nothing while costing a lot of processing time. The files are therefore stored rather than deflated. The point of the archive is convenience — one attachment instead of thirty — not size reduction. If you need the total to shrink, compress or resize the images first and then package them.