VBA Outline Levels: Set Range in Function

Found this function on mrexcel:
https://www.mrexcel.com/board/thread...evels.1061148/
It lets you switch between your outline levels:

Option Explicit
Public Function LowestRowGroupLevelDisplayed( _
      Optional ByVal Worksheet As Worksheet _
   ) As Long
   Dim Row As Range
   Dim LowestLevel As Long
   If Worksheet Is Nothing Then Set Worksheet = ActiveSheet
   For Each Row In Worksheet.UsedRange.Rows.EntireRow
      If Not Row.Hidden Then
         If Row.OutlineLevel > LowestLevel Then LowestLevel = Row.OutlineLevel
      End If
   Next Row
   LowestRowGroupLevelDisplayed = LowestLevel
End Function

Sub testGRp()
    If (LowestRowGroupLevelDisplayed = 1) Then
        ActiveSheet.Outline.ShowLevels RowLevels:=3
    Else
        ActiveSheet.Outline.ShowLevels RowLevels:=1
    End If
End Sub

The code expands/collapses all your groups at once, though.
Might there be a way to add an "input line" to set certain ranges of rows and columns?
To say e.g. "rows 4-6" or "columns K-L"?
(I haven't used any functions yet, I'm a bit overwhelmed.)

Right now, I hide/unhide specific rows and columns with a "Flip Switch":

' Flip alpha
Sub Flip_alpha()
   Dim Title As String
   Dim i As Integer
   Title = Range("A1")
   i = 0
   Do While Sheet1.Range("A1").Offset(0, i).Value <> Title
      i = i + 1
   Loop
   Sheet1.Range("A1").Range("A4:A8").Select
   ' Set Rows
   Selection.EntireRow.Hidden = Not Selection.EntireRow.Hidden
'   ' Set Columns
'   Selection.EntireColumn.Hidden = Not Selection.EntireColumn.Hidden
End Sub

This works just fine, but takes quite some time to build.
Set range, add rectangle (transparent) as button, create click, assign "call" to rectangle.
For every group. And in the end, it's not even the real deal, e.g. it leaves certain cells "selected" (screenshot).
And for now, this only allows me to switch between "Level closed" and "Level max expanded".
I'd have to have extra sets of macros for every level, right?
1) Set/Select range 2) Add rectangle 3) Create click 4) Assign to rectangle

I've attached the workbook, all codes included.
The merged cells with the double arrows are all working flip buttons, expanding and collapsing.

So now I wonder, if that function can be tweaked?
Might that result in less code?

Thank you for any help!