Program.cs

using DynamicData;
using System.Reactive.Concurrency;
using System.Reactive.Linq;

namespace ExpireAfterLeak;

internal class Program
{
    static void Main(string[] args)
    {
        var stopwatch = new System.Diagnostics.Stopwatch();
        stopwatch.Start();

        Console.WriteLine("Started");
        var subscription = Observable.Interval(TimeSpan.FromMilliseconds(250))
            .Select(x => new Item(x % 100))
            .Do(x => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} Creating Item with value {x.Value}"))
            .Take(5)

            //.Do(x => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} {stopwatch.ElapsedMilliseconds:D6} {string.Join('\n', x)}"), ex => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} {ex}"), () => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} Source Completed"))
            //.ToObservableChangeSet(x => x.Value, expireAfter: _ => TimeSpan.FromSeconds(10), scheduler: NewThreadScheduler.Default)

            //.ToObservableChangeSet(x => x.Value, scheduler: NewThreadScheduler.Default)
            //.Do(x => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} {string.Join('\n', x)}"), ex => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} {ex}"), () => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} Source Completed"))
            //.ExpireAfter(_ => TimeSpan.FromSeconds(10), pollingInterval: TimeSpan.FromSeconds(5), scheduler: NewThreadScheduler.Default)

            .ToObservableChangeSet(x => x.Value, scheduler: NewThreadScheduler.Default)
            .Do(x => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} {string.Join('\n', x)}"), ex => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} {ex}"), () => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} Source Completed"))
            .ExpireAfter(_ => TimeSpan.FromSeconds(10), scheduler: NewThreadScheduler.Default)

            .Subscribe(x => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} {string.Join('\n', x)}"), ex => Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} {ex}"), () =>
            {
                Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} Subscribe Completed");
                GC.Collect();
            });

        Console.ReadLine();
        Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} Dispose");
        subscription.Dispose();

        while (!Console.KeyAvailable)
        {
            GC.Collect();
            GC.WaitForPendingFinalizers();
            GC.Collect();
            Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6}  GC.Collect");
            Thread.Sleep(1000);
        }
        Console.WriteLine($"{stopwatch.ElapsedMilliseconds:D6} Exit");
    }
}

internal class Item
{
    public long Value { get; }

    public Item(long v) => Value = v;

    ~Item()
    {
        Console.WriteLine($"Item with value {Value} is being finalized.");
    }
}