https://stackoverflow.com/a/78092527/1271826

ImageDownloader.swift

extension ImageDownloader {
    // if you don't care about the order
    
    func downloadInRandomOrder() async -> [Image] {
        await withTaskGroup(of: Image.self) { group in
            let items = await fetchList()

            for item in items {
                group.addTask { await self.fetch(imageName: item.imageName) }
            }
            
            return await group.reduce(into: []) { $0.append($1) }
        }
    }
    
    // if you want them in order
    
    func downloadInOrder() async -> [Image] {
        await withTaskGroup(of: (Int, Image).self) { group in
            let items = await fetchList()
                                                    
            for (index, item) in items.enumerated() {
                group.addTask { await (index, self.fetch(imageName: item.imageName)) }
            }
            
            let dictionary = await group.reduce(into: [:]) { $0[$1.0] = $1.1 }
            return (0..<items.count).compactMap { dictionary[$0] }
        }
    }
       
    // Order independent result
    
    func downloadInOrder() async -> [String: Image] {
        await withTaskGroup(of: (String, Image).self) { group in
            let items = await fetchList()
        
            for item in items {
                group.addTask { await (item.imageName, self.fetch(imageName: item.imageName)) }
            }
            
            return await group.reduce(into: [:]) { $0[$1.0] = $1.1 }
        }
    }
}

Note, returning an array of Image and discarding the underlying ListItem (with a bunch of interesting properties) is a curious pattern. You probably would want to return both the ListItem and its associated Image.

Also, note that this pattern of retrieving all the Image is a bit of an antipattern. You generally want to fetch the image as needed. E.g., if there were 1000 ListItem, but you can only see 10 at any point in time, do you really want this to await the retrieval of all of the images? But there is not enough here to get specific on the solution, as we’d need info about ListItem, whether it is Identifiable or not, etc. But I just wanted to acknowledge the issues.

I noticed that the OP’s code did not assume that the imageName must be a URL, so I removed it from the above. Perhaps the OP’s fetch is building a URL from the imageName…