TryUpdateOrRemove extension method -- https://stackoverflow.com/a/72063401/11178549

ConcurrentDictionaryExtensions.cs

using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;

public static class ConcurrentDictionaryExtensions
{
    /// <summary>
    /// Uses the specified function to update a key/collection pair in the dictionary,
    /// if the key already exists. In case the function returns a null or empty
    /// collection, the key/collection pair is removed from the dictionary.
    /// In case the function returns the existing collection, the result is false.
    /// </summary>
    public static bool TryUpdateOrRemove<TKey, TCollection>(
        this ConcurrentDictionary<TKey, TCollection> source, TKey key,
        Func<TKey, TCollection, TCollection> updateValueFactory)
        where TCollection : class, ICollection
    {
        while (true)
        {
            if (!source.TryGetValue(key, out var existing))
                return false;

            var updated = updateValueFactory(key, existing);
            if (ReferenceEquals(updated, existing)) return false;

            if (updated is null || updated.Count == 0)
            {
                if (source.TryRemove(KeyValuePair.Create(key, existing))) return true;
            }
            else
            {
                if (source.TryUpdate(key, updated, existing)) return true;
            }
            // We lost the race to either TryRemove or TryUpdate. Try again.
        }
    }
}