workbook has no attribute 'add_chart'

i want to plot data, that i gathered in Python, in Excel.

And if the file already exists, it should just add another Sheet.

But when i try to add a file it gives me the Error "workbook" object has no attribute "add_chart"

Here is the code that i got:

import pandas as pd
import openpyxl
import xlsxwriter
from pathlib import Path

    def Convert(self):
        
        path_to_file = '{0}.xlsx'.format(self.Entry_ExcelName.get())
        path = Path(path_to_file)

        excel_file = '{0}.xlsx'.format(self.Entry_ExcelName.get())

        if path.is_file():
            writer = pd.ExcelWriter(excel_file, engine='openpyxl', mode='a')

        else: 
            writer  = pd.ExcelWriter(excel_file, engine='xlsxwriter')

        list_data_conv = self.list_data

        df=pd.DataFrame(list_data_conv)

        

        sheet_name = '{0}'.format(self.Entry_SheetName.get())
        df.to_excel(writer, sheet_name=sheet_name)

        workbook=writer.book
        worksheet=writer.sheets[sheet_name]

        chart=workbook.add_chart({'type': 'line'})
        
        i=len(list_data_conv)

        chart.add_series({
        'categories': ['{}'.format(sheet_name) ,1,1,i,1],
        'values':   ['{}'.format(sheet_name) ,1,2,i,2]
        })

        chart.set_x_axis({'name': 'Index', 'position_axis': 'on_tick'})
        chart.set_y_axis({'name': 'Value', 'major_gridlines': {'visible': False}})

        chart.set_legend({'position': 'none'})
        worksheet.insert_chart('D2', chart)

        writer.save()

I know there is already a similiar question like mine, however that has not fixed my problem.

I feel like i can't see the forest for the trees.