Hi All,

Here is VBA method to lock the cell after entering data in the cell.

Code:
Dim blnUnlockedAllCells As Boolean
Private Sub Worksheet_Change(ByVal Target As Range)
    
    Const RangeToLock As String = "A2:D1000" '<<  adjust to suit
    
    If Target.Cells.Count > 1 Then Exit Sub
    
    If Not blnUnlockedAllCells Then
        Me.Cells.Locked = False
        On Error Resume Next
        Me.Range(CStr(RangeToLock)).SpecialCells(2).Locked = True
        On Error GoTo 0
        blnUnlockedAllCells = True
        Me.Protect Password:="pwd", userinterfaceonly:=True
    End If
    
    If Not Application.Intersect(Target, Me.Range(CStr(RangeToLock))) Is Nothing Then
        If Len(Target) Then Target.Locked = True
    End If
    
End Sub
Note: adjust the RangeToLock to suit. This code goes in the sheet module of the sheet in question.

I hope this helps !