public class ParentViewModel
{
    public string Data { get; set; }
}

<ChildComponent ParentViewModel="parentViewModel" OnDataChanged="HandleDataChanged" />

@code {
    private ParentViewModel parentViewModel = new ParentViewModel();

    private void HandleDataChanged(string data)
    {
        parentViewModel.Data = data;
    }
}

public partial class ChildComponent
{
    [Parameter]
    public ParentViewModel ParentViewModel { get; set; }

    [Parameter]
    public EventCallback<string> OnDataChanged { get; set; }

    private string childData;

    private async Task HandleButtonClick()
    {
        await OnDataChanged.InvokeAsync(childData);
    }
}

<div>
    <input type="text" bind="@childData" />
    <button @onclick="HandleButtonClick">Send Data to Parent</button>
</div>