Here's an example of animation() using value. Paste into Playgrounds.

// Example for Paul Lee
// 2022.01.29
// Animation using Value.
import SwiftUI
import PlaygroundSupport
struct AnimationTest: View {
    // Think of animationAmount as a light switch
    // The view has one look when value is 1.0 and a different look when value is 1.5
    @State private var animationAmount = 1.0
    var body: some View {
        Button("Tap Me") {
            // important button function here
        }
        .padding(50)
        .background(.yellow)
        .clipShape(Circle())
        .overlay(
            Circle()
                .stroke(.indigo)
                .scaleEffect(animationAmount)
                .opacity(1.5 - animationAmount)
            // value tells SwiftUI to render scale and opacity between 1.0 and 1.5
            // SwiftUI determines how many frames to render based on duration
                .animation(
                    .easeInOut(duration: 1)
                        .repeatForever(autoreverses: false),
                    value: animationAmount
                )
        )
        .onAppear {
            // Switch the value to 1.5
            // The view has a different look when the value is 1.5
            animationAmount = 1.5
        }
    }
}

PlaygroundPage.current.setLiveView(AnimationTest().frame(width: 300, height: 300))

In this example, think of animationAmount as a light switch. When the switch has one value, SwiftUI renders the view one way. When the switch gets a different value, the view is rendered another way. SwiftUI sees these two views as the start and ending point of the animation and will render all the frames in between.

In your code, you need to think what the starting view looks like ( i.e. Placeholder = color.red ) and what the ending view looks like (perhaps the final, fetched image?)

Maybe you have a computed boolean? imageIsLoaded, for example? It's false to start, and is true when the images is fetched and loaded. Consider using this as your "light switch" ? When the value changes, it triggers your animation.

Let us know what worked for you.