If you do use a third party plugin on photos uploaded through “Envato Wordpress Plugin”, it does work, but then, those medias are not automaticaly attached to post (because of the old big size)
You need to run the plugin after the upload. If the theme supports custom size it shouldn’t be a problem with or without plugin. You can check the upload folder ( wp-content/uploads/2023/10/ ) to see if there’s any image resized.
Resize plugin does work perfectly, i can see my resizes images immediately on the upload folder (.jpg original + resize+ webp). But in this case medias are not automaticaly attached to post.
Trying to test, i downloaded/resized a picture myself on my computer, then uploaded manualy to “media” and here, it does work, medias are attached to post.