第一名

Range对象已将工作表作为父级包含。

Sub fCopyPasteValues(sourceSheet As Worksheet, targetSheet As Worksheet, sourceRange As Range, targetRange As Range)
    
        sourceRange.Select   '<-------------- THIS is where i get the Error, saying method or dataobjet not found! refering to sourceRange

        Range(Selection, Selection.End(xlDown).End(xlToRight)).Select
        Selection.Copy
        targetRange.PasteSpecial Paste:=xlPasteValuesAndNumberFormats, Operation:= _
        xlNone, SkipBlanks:=False, Transpose:=False
        Application.CutCopyMode = False
        targetRange.NumberFormat = "m/d/yyyy"
    
End Sub

第二名

或者，一种更简洁的方式来完成函数所做的一切。
此外，我将其更改为函数，并使其更加稳定：

Public Function fCopyVerfügbarkeitenData()

    Dim sourceRange As Range
    Dim targetRange As Range
    Dim sourceSheet As Worksheet
    Dim targetSheet As Worksheet
    
    Set sourceRange = Sheets("sheet1").Range("A4")
    Set targetRange = Sheets("sheet1").Range("A2")
    Set sourceSheet = Sheets("Verfügbarkeit_Daten")
    Set targetSheet = Sheets("Verfügbarkeiten")
    
    
    sourceSheet.Visible = True
    sourceSheet.Activate
    Call Tabelle18.refreshVerfuegbarkeiten
    
    fCopyPasteValues sourceRange, targetRange
    sourceSheet.Visible = False
                    
End Function

Function fCopyPasteValues(sourceRange As Range, targetRange As Range)
        
        ' Width and Height
        Dim W As Long
        Dim H As Long
        
        ' Find Outer Bounds
        H = sourceRange.End(xlDown).Row - sourceRange.Row + 1
        W = sourceRange.End(xlToRight).Column - sourceRange.Column + 1
        
        ' Error handing in case region is only 1 cell wide or high
        If H > 100000 Then H = 1
        If W > 100000 Then W = 1
        
        ' Copy and reformat Action
        targetRange.Resize(H, W).Value = sourceRange.Resize(H, W).Value
        targetRange.NumberFormat = "m/d/yyyy"
        
End Function