BlazorFiddle - Blazor .Net Developer Playground and Code Editor in the Browser.

Index

@page "/"

@inject HttpClient Http
@inject IJSRuntime JS

<div>
    @foreach(var imageSrc in ImageSources)
    {
        <div>
            <img hidden="@(!imageSrc.Loaded)" id="@imageSrc.Id" />
            @if(!imageSrc.Loaded)
            {
                <span>Loading...</span>
            }
        </div>
    }
</div>

@code {
    private List<ImageSource> ImageSources = new(){
        new(Guid.NewGuid(), "https://picsum.photos/200/300"),
        new(Guid.NewGuid(), "https://picsum.photos/200/300"),
        new(Guid.NewGuid(), "https://picsum.photos/200/300"),
        new(Guid.NewGuid(), "https://picsum.photos/200/300")
    };

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if(firstRender)
        {
            foreach(var imageSrc in ImageSources)
            {
                var stream = await Http.GetStreamAsync(imageSrc.Url);
                await SetImage(imageSrc.Id.ToString(), stream);
                imageSrc.Loaded = true;
                await InvokeAsync(StateHasChanged);
            }
        }
    }
    public async Task SetImage(string imageElementId, Stream imageStream)
    {
        await Task.Delay(1000);
        var dotnetImageStream = new DotNetStreamReference(imageStream);
        await JS.InvokeVoidAsync("setImage", imageElementId, dotnetImageStream);
    }

    public record ImageSource(Guid Id, string Url)
    {
        public bool Loaded {get;set;}
    }
}

namespace BlazorFiddleProject
{
    using Microsoft.Extensions.DependencyInjection;


    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
        }

        // Warning: IComponentsApplicationBuilder - not the original .NET 6.0 interface. This was done to make old saves work. 
        public void Configure(IComponentsApplicationBuilder app)
        {
            app.AddComponent<App>("app");
        }
    }
}

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8"/>
    <meta name="viewport" content="width=device-width">
    <title>BlazorFiddleProject</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">

    <link href="_content/MatBlazor/dist/matBlazor.css" rel="stylesheet" />
    <script src="_content/MatBlazor/dist/matBlazor.js"></script>    

    <style>
        app { }
    </style>

    <script type="text/javascript">
    </script>
</head>
<body>
<app>Loading...</app>

<script src="_framework/blazor.webassembly.js"></script>
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
<script>
  window.setImage = async (imageElementId, imageStream) => {
    const arrayBuffer = await imageStream.arrayBuffer();
    const blob = new Blob([arrayBuffer]);
    const url = URL.createObjectURL(blob);
    const image = document.getElementById(imageElementId);
    image.onload = () => {
      URL.revokeObjectURL(url);
    }
    image.src = url;
  }
</script>
</body>
</html>

BlazorFiddle was updated from Blazor 0.7 to .NET 6.0. Your old source code could not work. You need to upgrade to latest.