I was wondering if External Images supports image optimization plugins. Specifically, they reduce image file sizes, some also convert images to webp format for faster loading time. Depending on plugin features, conversion can be manual (on request) and/or automated (cron).
No – because the images are not stored on your server it’s not really an option to smush the images.
There is one option to use an image resizing function from WordPress.org, but in general image optimisation doesn’t work for external images – the images are not stored on your server.