Backdate a task?
(closed account) says:
Nope. Set a non repeating task to the desired due date. Set a 90 day repeating task also set to the desired due date. On that day you'll complete both of them.
(closed account) says:
Maybe I'm missing a detail, but why can't you just create a task with a due date of Dec 19, 2020 and the repeat setting of "every 90 days"? Then complete the task. I just did this with a test task and the next due date is March 19.
You can set any date, past or future, as the due date.
You can set any date, past or future, as the due date.