It’s not currently possible - although Wix does some compression, and conversion when serving media to live sites (e.g. to AVIF), but it’s likely not as far as you’ll get with external tools.
It’s recommended to upload images as AVIF, which is a newer type of image file, better than JPEG and approximately 50% smaller than WebP.
You can read more about optimizing media here - Site Performance: Optimizing Site Media | Help Center | Wix.com.