Thanks to jwenzel and other posts I did find a solution which I want to publish here, so that others do not have to read all the information.

Put either one of the solutions into Program.cs right under

var builder = WebApplication.CreateBuilder(args);

Solution1 Source: How to call .UseStaticWebAssets() on WebApplicationBuilder?

if (builder.Environment.IsEnvironment("DevelopmentPK"))
{
    builder.WebHost.UseWebRoot("wwwroot").UseStaticWebAssets();
}

Solution2 Source: Unable to call StaticWebAssetsLoader.UseStaticWebAssets

if (builder.Environment.IsEnvironment("DevelopmentPK"))
{
    StaticWebAssetsLoader.UseStaticWebAssets(builder.Environment, builder.Configuration);
}

Replace DevelopmentPK with the name of your Environment, defined in launchSettings.json.

"environmentVariables": {
  "ASPNETCORE_ENVIRONMENT": "DevelopmentPK"
}