I would like to have a rule to change the task progress from “Waiting” to “Not started” when all linked tasks are in a specific section or when all linked task are completed.
It maybe can result in 2 different rules, but I do not know how to configure this.
That wouldn’t be possible as you’ve described it. Think of rules generally as operating on one task only as the trigger to fire the rule and the destination for some action to take effect, not across many tasks. An exception is sometimes (limited) regarding the subtasks of the triggered task.
You could try explaining your overall need, but it would result in a recommendation for a different implementation that you have chosen already, I’d think.