<PackageReference Include="System.Reactive" Version="6.0.2" />

System.Reactive.Subjects.ReplaySubject<T>

public sealed class ReplaySubject<T> : SubjectBase<T>
Represents an object that is both an observable sequence as well as an observer. Each notification is broadcasted to all subscribed and future observers, subject to buffer trimming policies.
namespace System.Reactive.Subjects { public sealed class ReplaySubject<[System.Runtime.CompilerServices.Nullable(2)] T> : SubjectBase<T> { public ReplaySubject(); public ReplaySubject(IScheduler scheduler); public ReplaySubject(int bufferSize); public ReplaySubject(int bufferSize, IScheduler scheduler); public ReplaySubject(TimeSpan window); public ReplaySubject(TimeSpan window, IScheduler scheduler); public ReplaySubject(int bufferSize, TimeSpan window); public ReplaySubject(int bufferSize, TimeSpan window, IScheduler scheduler); } }