Detect a ResizeForm click (Not Just RESIZE!!)

You can Subclass your Window.

Code for Module

Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long
Declare Function SetWindowLong& Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long)
Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal msg As Long, ByVal wparam As Long, ByVal lparam As Long) As Long

Const WM_COMMAND = &H111
Const WM_CLOSE = &H10
Const GWL_WNDPROC = (-4)
Const WM_ENTERSIZEMOVE = &H231

Global WndProcOld As Long

Public Function WindProc(ByVal hwnd As Long, ByVal wMsg As Long, ByVal wparam As Long, ByVal lparam As Long) As Long

    If wMsg& = WM_ENTERSIZEMOVE Then
        '***Place code here***
        MsgBox "Resize"
    End If
    
    WindProc = CallWindowProc(WndProcOld&, hwnd&, wMsg&, wparam&, lparam&)
    
End Function

Sub Subclass(hwnd As Long)
    WndProcOld& = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf WindProc)
End Sub

Sub UnSubclass(hwnd)
    SetWindowLong hwnd, GWL_WNDPROC, WndProcOld&
    WndProcOld& = 0
End Sub

Code for Form

Private Sub Form_Load()
    Subclass Me.hwnd
End Sub

Private Sub Form_Unload(Cancel As Integer)
    UnSubclass Me.hwnd
End Sub