I'm not sure your existing formula makes sense. Since this is a scheduled flow, when it runs there's no context of whether something changed or not as the record hasn't undergone an update or anything. It's just a scheduled action (query) on records in your instance.
ISCHANGED()
is useful in record-triggered flows where the records in the transaction have had an update and can compare the prior value with the current value.
Now, to your specific question, there's many ways to do this.
Going off using a scheduled flow, I'd suggest creating an extra custom field titled Last Status Changed Date
on the object.
This would require you to create a separate flow/trigger/automation for the object to stamp this custom date field whenever the Status changes.
Then, in this flow you could add a formula to check how many days the Status has been unchanged
{!$Flow.CurrentDate} - {!Record.Last_Status_Changed_Date__c} > 5
.