There is a new option added in Odoo 15, which helps create sub-tasks in the project task.
There is one new option included to create the recurrent task.
When you click on that option, you will find a new page under that task with the name “Recurrence’ Where you can set recurrence of day, dates, Etc.
In This Recurrence section, you have the option to set recurrence for a task. It allows you to set the task by Month, Year, Date, Day of Week. Besides, you can also set a number of repetitions, till the end date or forever. You can view the future occurrence of the task based on your selection.