Knowing if it's an app, a physical product, or a service will help me give you a much more specific feature idea.
: Build a "Comment Mode" directly into the prototype UI. This allows testers to click on any element and leave a digital sticky note, turning the prototype itself into a collaborative research tool. ProtГіtipo
Since is the Portuguese word for "Prototype," I can suggest a high-impact feature for a prototype depending on what you are building. Knowing if it's an app, a physical product,