COUNTIF Function
From Planfix
The COUNTIF function allows you to count the number of items in a list that meet a specific condition.
Format
COUNTIF(Repeating variable; Conditional expression)
Example
Counting the number of subtasks in a specific status:
COUNTIF({{Task.Subtasks}}; {{Task.Subtasks.Status}}="In Progress")
Result: the number of subtasks with the status "In Progress"