Two different problems
Oversized dimensions (more pixels than anything ever displays) are fixed by scaling. Heavy files are fixed by compression. The list filters show both.
Choose values per run
When scaling or compressing, the plugin asks for target width or quality, prefilled with your defaults. The settings page only controls defaults and what happens to new uploads.
Guarantees
A backup is always taken first. If the result is larger than the original (happens with already-optimized images), the image is automatically reverted and you get a warning instead of a worse file.
WebP
WebP files are created alongside the originals and served via picture tags — works on every server with zero configuration. Enable delivery under Settings → Compression.