Dynamic data validation list

It can be dynamically update (via VBA imho) but in other way that's why is called validation, you can't enter not proper value

I said imho, I am not sure. I'll think about it.

An example of what? What are you asking for? A sample workbook?

Pl upload a sample file.

OK. I figured out something like this.

Dynamic range for drowdown list with 1 additional empty line at bottom (to give user possibility put number outside validation list)
If this 'typed' value does not exist already is added at the bottom and automatically appear at second click in cell on drop down list.

1. VBA into particular sheet:

Private Sub Worksheet_Change(ByVal Target As Range)
Dim lastRow As Long
lastRow = ActiveSheet.Cells(Rows.Count, 1).End(xlUp).Row
If Not Intersect(Target, Range("C1")) Is Nothing Then
    With ActiveSheet.Range("A1:A30")
        Set c = .Find(Target, LookIn:=xlValues)
        If Not c Is Nothing Then
            Exit Sub
        Else
            Range("A" & lastRow + 1) = Target.Value
        End If
    End With
End If
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim lastRow As Long
lastRow = ActiveSheet.Cells(Rows.Count, 1).End(xlUp).Row
If Not Intersect(Target, Range("C1")) Is Nothing Then
    With [C1].Validation
        .Delete
        .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _
        xlBetween, Formula1:="=list"
        .IgnoreBlank = True
        .InCellDropdown = True
        .InputTitle = ""
        .ErrorTitle = ""
        .InputMessage = ""
        .ErrorMessage = ""
        .ShowInput = True
        .ShowError = True
    End With
End If
End Sub

2. dynamic range to create A1:A30 called 'list'
3. drodown in cell C1

and should works

file attached.

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