Legally, often no. Practically, sometimes yes. If you already understand clipping, spacing, fall consequences, and how your head reacts to exposure, a well-chosen easy route does not require a guide. If this will be your first ferrata day, the first half-day with a guide is the fastest way to avoid basic mistakes.
The honest dividing line is not courage. It is whether you can move efficiently without panicking at each anchor. Many hikers are strong enough for easy ferratas but still move too slowly and too erratically to be safe on a busy route the first time out.