Odoo 13 EE & CE doesn't have this feature. It's now available in Odoo 15 EE through Work Entries.

But you have work a rounds you can create a salary rule in your structure to calculate the "Out of Contract".
You can use a python code rule to get the  Gross and divide it by the days of the month to get the value of 1 salary pay day then use an input to deduct the out of contract days.

For Example:
    result = - ( (GROSS divided by 30) * inputs.OUT_OF_CONTRACT.amount)