感谢@ Hans Passant 在主要问题的评论中提出的建议，该方法可以正常工作:

Thanks to what @Hans Passant suggested in his commentary in the main question, this is working as expected:

Public Function GetEventHandlers(component As IComponent, eventName As String) As IReadOnlyCollection(Of [Delegate])

    Dim componentType As Type = component.GetType()

    ' Find event declaration in the source type.
    Dim eventInfo As EventInfo = componentType.GetEvent(eventName, BindingFlags.ExactBinding Or BindingFlags.Instance Or BindingFlags.NonPublic Or BindingFlags.Public Or BindingFlags.Static)
    If (eventInfo Is Nothing) Then
        Throw New ArgumentException($"Event with name '{eventName}' not found in type '{componentType.FullName}'.", NameOf(eventName))
    End If

    ' The type on which the event is declared.
    Dim declaringType As Type = eventInfo.DeclaringType

    ' Find event-field declaration in the declaring type.
    Dim eventField As FieldInfo = Nothing

    ' Possible namings for an event field.
    Dim eventFieldNames As String() = {
        $"Event{eventName}",            ' Fields declared in 'System.Windows.Forms.Control' class.
        $"EVENT_{eventName.ToUpper()}", ' Fields declared in 'System.Windows.Forms.Form' class.
        $"{eventName}Event"             ' Fields (auto-generated) declared in other classes.
    }

    For Each name As String In eventFieldNames
        eventField = declaringType.GetField(name, BindingFlags.DeclaredOnly Or BindingFlags.ExactBinding Or BindingFlags.IgnoreCase Or BindingFlags.Instance Or BindingFlags.NonPublic Or BindingFlags.Static)
        If (eventField IsNot Nothing) Then
            Exit For
        End If
    Next name

    If (eventField Is Nothing) Then
        Throw New ArgumentException($"Field with name '{String.Join("' or '", eventFieldNames)}' not found in declaring type '{declaringType.FullName}'.", NameOf(eventName))
    End If

#If DEBUG Then
    Debug.WriteLine($"Field with name '{eventField.Name}' found in declaring type '{declaringType.FullName}'")
#End If

    Dim eventFieldValue As object = eventField.GetValue(component)
    If TypeOf eventFieldValue Is MulticastDelegate
        ' See @Hans Passant comment:
        ' https://***.com/questions/56763972/get-all-the-event-handlers-of-a-event-declared-in-a-custom-user-control?noredirect=1#comment100177090_56763972

        Return DirectCast(eventFieldValue, MulticastDelegate).GetInvocationList()
    End If

    Dim eventsProp As PropertyInfo = GetType(Component).GetProperty("Events", BindingFlags.DeclaredOnly Or BindingFlags.ExactBinding Or BindingFlags.Instance Or BindingFlags.NonPublic, Type.DefaultBinder, GetType(EventHandlerList), Type.EmptyTypes, Nothing)
    Dim eventsPropValue As EventHandlerList = DirectCast(eventsProp.GetValue(component, BindingFlags.Default, Type.DefaultBinder, Nothing, CultureInfo.InvariantCulture), EventHandlerList)
    Dim eventDelegate As [Delegate] = eventsPropValue.Item(eventFieldValue)
    Dim invocationList As [Delegate]() = eventDelegate?.GetInvocationList()

    If (invocationList Is Nothing) Then ' There is no event-handler registered for the specified event.
       Return Enumerable.Empty(Of [Delegate]).ToList()
    End If

    Return invocationList

End Function

我们还可以为 EventInfo 类型定义下一个方法扩展，以充当

Also we can define the next method extension for EventInfo type to act as a method overload for EventInfo.RemoveEventHandler(Object, Delegate):

''' ----------------------------------------------------------------------------------------------------
''' <summary>
''' Removes an event handler from an event source.
''' </summary>
''' ----------------------------------------------------------------------------------------------------
''' <example> This is a code example.
''' <code>
''' Public Class Form1
''' 
'''     Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Shown
'''         Dim target As Form = Me
'''         Dim eventInfo As EventInfo = target.GetType().GetEvent(NameOf(Form.Click))
'''         eventInfo.RemoveEventHandler(target, NameOf(Me.Form1_Click))
'''     End Sub
''' 
'''     Private Sub Form1_Click(sender As Object, e As EventArgs) Handles MyBase.Click
'''         MsgBox(MethodBase.GetCurrentMethod().Name)
'''     End Sub
''' 
''' End Class
''' </code>
''' </example>
''' ----------------------------------------------------------------------------------------------------
''' <param name="eventInfo">
''' The event information.
''' </param>
''' 
''' <param name="target">
''' The event source.
''' </param>
''' 
''' <param name="handlerName">
''' The name of the delegate to be disassociated from the events raised by <paramref name="target"/>.
''' <para></para>
''' Note that the name is case-sensitive.
''' </param>
''' ----------------------------------------------------------------------------------------------------
<Extension>
Public Sub RemoveEventHandler(eventInfo As EventInfo, target As IComponent, handlerName As String)

    If String.IsNullOrWhiteSpace(handlerName)
        Throw New ArgumentNullException(NameOf(handlerName))
    End If

    For each handler As [Delegate] in GetEventHandlers(target, eventInfo.Name)
        If handler.Method.Name.Equals(handlerName, StringComparison.Ordinal)
            eventInfo.RemoveEventHandler(target, handler)
            Exit Sub
        End If
    Next handler
    Throw New ArgumentException($"No delegate was found with the specified name: '{handlerName}'", NameOf(handlerName))

End Sub