Hi CorTax,

Thanks for your help. I have changed the line to the one you suggested. I do not get the error anymore.

But now the code raises UserError('couldnt create book object!').

the code is now the following:

from odoo import api, fields, models, _
from odoo.exceptions import UserError, ValidationError
import logging
import tempfile
import binascii

from datetime import datetime

_logger = logging.getLogger(__name__)


try:
    import xlrd
except ImportError:
    _logger.debug('Cannot `import xlrd`.')



class ImportExcel(models.TransientModel):

    _name = "import.excel.wizard"
    _description = "Wizard to import excel data"

    data = fields.Binary('file')
    name_of_file = fields.Char(string="File name")

    def get_product(self, value):
        product = self.env['product.template'].search([('name', '=', value)])
        return product.id if product else False


    def import_file(self):

        
        file_name = self.name_of_file.lower()

        sale_order_view = False

        if file_name.strip().endswith('.xlsx'):
            try:
                fp = tempfile.NamedTemporaryFile(delete=False, suffix=".xlsx")

            except:
                raise UserError('couldnt create file')
            try:
                fp.write(binascii.a2b_base64(self.data))

            except:
                raise UserError('couldnt write data')
            try:
                fp.seek(0)
            except:
                raise UserError('couldnt seek 0')
            values = {}
            try:
                workbook = xlrd.open_workbook(fp.name)

            except:
                raise UserError(f'couldnt create book object {fp.name}, for the following data: {self.data}')
            try:
                sheet = workbook.sheet_by_index(0)
            except:
                raise UserError('couldnt create sheet object')
            #except:
                #raise UserError(_("Invalid file!"))

            vals_list = []

            for row_no in range(sheet.nrows):
                val = {}
                values = {}
                if row_no <= 0:
                    fields = map(lambda row: row.value.encode('utf-8'), sheet.row(row_no))
                    _logger.debug("hello there people")
                else:
                    line = list(map(lambda row: isinstance(row.value, bytes) and row.value.encode('utf-8') or str(row.value), sheet.row(row_no)))
                    values.update({
                        'product_id': self.get_product(line[0]),
                        'name': line[1],
                        'product_uom_qty': line[2]
                    })
                    vals_list.append((0, 0, values))

            sale_order_values = {
                'order_line': vals_list
            }

            if len(vals_list) != 0:
                sale_order = self.env['sale.order'].search([('name', '=', self.env.context.get('active_id'))])
                sale_order_view = sale_order.write(sale_order_values)

            if sale_order_view:
                return {
                    'type': 'ir.actions.act_window',
                    'res_model': 'sale.order',
                    'view_mode': 'form',
                    'res_id': sale_order_view.id,
                    'views': [(False, 'form')],
                }
        else:
            raise ValidationError(_("Unsupported File Type"))

Solved the issue. xlrd module doesn't work for xlsx files anymore.