How to Make a Cell Read only depending upon Value of another cell

Do right click on sheet tab and select view code and paste the below code. Return to excel and check…

Private Sub Worksheet_Change(ByVal Target As Range)

If Target.Count > 1 Then Exit Sub
If Target.Column > 2 Then Exit Sub

If Target.Column = 2 Then
    With Target.Offset(, -1)
        If .Value = "" Or .Value < 2 Then
            Application.EnableEvents = False
                Target.ClearContents
            Application.EnableEvents = True
            
            MsgBox "Column-A value is less than 2 So Entry is not allowed here...", vbInformation, "Restricted Entry"
        End If
    End With
Else
    If Target.Value < 2 Then
        Application.EnableEvents = False
            Target.Offset(, 1).ClearContents
        Application.EnableEvents = True
    End If
End If

End Sub

Hi and welcome to the forum

You could also use Data Validation for this, using A as the criteria.