Unable to save resized images with Preview

I've tried several times, unsuccessfully, to reduce the size of a photo from 3.3MB to under 2MB so I can upload it to a website.

As per Apple instructions, I'm opening it in Preview, going to the Adjust Size tab, reducing the value of the resolution so that the resulting image size is under 2MB, then hitting 'OK'. It's worth noting here that, on later attempts, it became very sluggish in recalculating the size, as if the app is failing.

When I go to save the edited file, however, I'm (a) not given a 'Save as...' option in the drop-down menu, so I can only overwrite the existing file - even if I change its name. And (b), when I go to the 'resaved' file in its folder, it still has a size of 3.3MB, whatever I do.

I'm using the Catalina OS, and the file folder is located in iCloud, if this is significant. Can anyone tell me where I might be going wrong?