<h3>Without Workaround</h3>

<TelerikTreeView Data="@FlatData"
                 @bind-CheckedItems="@CheckedItems"
                 @bind-ExpandedItems="@ExpandedItems"
                 @bind-SelectedItems="@SelectedItems"
                 CheckBoxMode="@TreeViewCheckBoxMode.Multiple"
                 SelectionMode="@TreeViewSelectionMode.Multiple" />

<h3>With Workaround</h3>

<TelerikTreeView Data="@FlatData"
                 CheckedItems="@CheckedItems"
                 CheckedItemsChanged="@TreeViewCheckedItemsChanged"
                 @bind-ExpandedItems="@ExpandedItems"
                 SelectedItems="@SelectedItems"
                 SelectedItemsChanged="@TreeViewSelectedItemsChanged"
                 CheckBoxMode="@TreeViewCheckBoxMode.Multiple"
                 SelectionMode="@TreeViewSelectionMode.Multiple" />

@code {
    private IEnumerable<TreeItem> FlatData { get; set; } = new List<TreeItem>();
    private IEnumerable<object> CheckedItems { get; set; } = new List<TreeItem>();
    private IEnumerable<object> ExpandedItems { get; set; } = new List<TreeItem>();
    private IEnumerable<object> SelectedItems { get; set; } = new List<TreeItem>();

    private bool ShouldAllowSelectionChange { get; set; } = true;

    private Random rnd { get; set; } = new Random();

    private async Task TreeViewCheckedItemsChanged(IEnumerable<object> newCheckedItems)
    {
        CheckedItems = newCheckedItems;
        ShouldAllowSelectionChange = false;
    }

    private async Task TreeViewSelectedItemsChanged(IEnumerable<object> newSelectedItems)
    {
        // Use only if TreeViewSelectedItemsChanged executes before ТreeViewCheckedItemsChanged
        //await Task.Delay(1);

        if (ShouldAllowSelectionChange)
        {
            SelectedItems = newSelectedItems;
        }
        else
        {
            ShouldAllowSelectionChange = true;
        }
    }

    protected override void OnInitialized()
    {
        FlatData = LoadFlat();

        ExpandedItems = FlatData.Where(x => x.HasChildren == true);
    }

    #region TreeView data generation

    private int TreeLevels { get; set; } = 2;
    private int ItemsPerLevel { get; set; } = 2;
    private int IdCounter { get; set; } = 1;

    private List<TreeItem> LoadFlat()
    {
        List<TreeItem> items = new List<TreeItem>();

        PopulateTreeItems(items, null, 1);

        return items;
    }

    private void PopulateTreeItems(List<TreeItem> items, int? parentId, int level)
    {
        for (int i = 1; i <= ItemsPerLevel; i++)
        {
            var itemId = IdCounter++;
            items.Add(new TreeItem()
            {
                Id = itemId,
                Text = $"Level {level} Item {i} Id {itemId}",
                ParentId = parentId,
                HasChildren = level < TreeLevels
            });

            if (level < TreeLevels)
            {
                PopulateTreeItems(items, itemId, level + 1);
            }
        }
    }

    #endregion

    public class TreeItem
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public bool HasChildren { get; set; }
        public string Text { get; set; } = string.Empty;
        public object? Icon { get; set; }
    }
}