Facilities to help a generic host terminate once all BackgroundServices are done with their work.

BackgroundServiceLifetime.cs

/// <summary>
/// Provides lifetime management for background services, ensuring proper cleanup and termination.
/// </summary>
/// <remarks>This is context aware and will only activate if it detects the host is not a web application.</remarks>
/// <param name="lifetime">The application lifetime manager.</param>
/// <param name="scopeFactory">The factory for creating service scopes.</param>
public class BackgroundServiceLifetime(IHostApplicationLifetime lifetime, IServiceScopeFactory scopeFactory) : BackgroundService
{
    private readonly IHostApplicationLifetime _lifetime = lifetime; // Application lifetime manager.
    private readonly IServiceScopeFactory _scopeFactory = scopeFactory; // Factory for creating service scopes.

    /// <summary>
    /// Executes the background service asynchronously.
    /// </summary>
    /// <param name="stoppingToken">The token to monitor for cancellation requests.</param>
    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        await using var scope = _scopeFactory.CreateAsyncScope(); // Create a new service scope.

        if (scope.ServiceProvider.GetService<IWebHostEnvironment>() is not null)
            return;

        var services = scope
            .ServiceProvider
            .GetServices<IHostedService>()
            .Where(m => m is BackgroundService && m != this)
            .Cast<BackgroundService>(); // Retrieve all hosted background services.

        // Wait until all background services are initialized.
        // Not many ways to be reactive here, since there are no notifications.
        while (services.Any(m => m is { ExecuteTask: null }))
            await Task.Delay(TimeSpan.FromMilliseconds(10), stoppingToken);

        // Wait for tasks of all other background services.
        foreach (var service in services.Select(m => m.ExecuteTask))
            await service!.ConfigureAwait(ConfigureAwaitOptions.SuppressThrowing);

        _lifetime.StopApplication(); // Stop the application gracefully once all background services are done.
    }
}

public static class ServiceCollectionExtensions
{
    /// <summary>
    /// Add an <see cref="BackgroundServiceLifetime"/> registration that monitors other background services and 
    /// stops the application when no <see cref="BackgroundService"/> is running.
    /// </summary>
    /// <param name="services"></param>
    /// <returns></returns>
    public static IServiceCollection AddBackgroundServiceLifetime(this IServiceCollection services)
    {
        return services.AddHostedService<BackgroundServiceLifetime>();
    }
}