The entered 20 19-8-5 will be recognized as a date format, so it will be converted to the default date display mode of 20 19/8/5. Enter the cell format. In the classification, the date has the form of 20 19-8-5 you want.

However, this format will add a virtual zero to the months and days below ten, which can be further set as a custom format, as shown in the figure below, so as to get the results you want.