Webflow content editor doesn’t currently let user upload images to different states, I am trying to implement a collections list that lets the BG image change dynamically on different states
You could only pull this off with custom code. You would have to use multiple image fields (for each viewport), upload the correctly sized image for each, then in your template check the viewport width, if breakpoint = X, assign the src value from a hidden element bound to the field, to the element background property you wanted to target. There would be no preview. It would only work on a published page.
If you are not a coder, you may want to use the freelance category and post a gig.