LRU Cache C# Data Structure

LruCache.cs

public class LruCache<TKey, TValue> where TKey : IEquatable<TKey>
{
    #region Private Types
    private struct Entry
    {
        public TKey Key { get; set; }
        public TValue Value { get; set; }
    }
    #endregion
    
    #region Private Fields
    private readonly SortedList<DateTime, Entry> _entries = new SortedList<DateTime, Entry>();
    private readonly Dictionary<TKey, DateTime> _keyToTimestamps = new Dictionary<TKey, DateTime>();
    private int _capacity = 100;
    #endregion

    #region Public Properties
    public int Count => _entries.Count;
    public int Capacity
    {
        get => _capacity;
        set
        {
            _capacity = value;
            if (_capacity <= 0)
            {
                Clear();
                return;
            }
            while (Count > _capacity)
                RemoveEarliest();
        }
    }
    #endregion

    #region Public Methods
    public void Clear()
    {
        _entries.Clear();
        _keyToTimestamps.Clear();
    }

    public DateTime Add(TKey key, TValue val)
    {
        if (Capacity <= 0)
            return default;
        if (Count == Capacity)
            RemoveEarliest();
            
        var timestamp = DateTime.Now;
        _entries.Add(timestamp, new Entry { Key = key, Value = val });
        _keyToTimestamps.Add(key, timestamp);
        return timestamp;
    }

    public bool TryGet(TKey key, out DateTime timestamp, out TValue val)
    {
        if (!_keyToTimestamps.TryGetValue(key, out timestamp))
        {
            val = default;
            return false;
        }
        val = _entries[timestamp].Value;
        return true;
    }
    
    public bool Remove(TKey key)
    {
        if (!_keyToTimestamps.Remove(key, out var timestamp))
            return false;
        _entries.Remove(timestamp);
        return true;
    }

    public TValue RemoveEarliest()
    {
        var lruEntry = _entries.Values[0];
        _entries.RemoveAt(0);
        _keyToTimestamps.Remove(lruEntry.Key);
        return lruEntry.Value;
    }

    public bool RemoveEarliest(out DateTime timestamp, out TValue val)
    {
        timestamp = default;
        val = default;
        
        if (_entries.Count == 0)
            return false;
        
        var lruEntry = _entries.Values[0];
        val = lruEntry.Value;
        timestamp = _keyToTimestamps[lruEntry.Key];
        
        _entries.RemoveAt(0);
        _keyToTimestamps.Remove(lruEntry.Key);
        return true;
    }
    #endregion
}