If you're a business owner who wants to analyze how users arrive at your website and app, as well as the user journeys across both of these platforms, what should you use to generate insights?

You should use Google Analytics 4 properties. A GA4 property can collect data from a website and from iOS and Android apps into the same property through separate data streams, and because everything is recorded using one event-based data model, journeys can be followed across platforms rather than analysed in isolation. That is the core design difference from the older Universal Analytics model, which kept web and app data apart. In practice it means a single property can answer questions like how many people discovered the brand on the website and later converted in the app, which acquisition sources bring in cross-platform users, and where the journey breaks between the two. Reports such as acquisition, plus the Explore workspace for path and funnel analysis, are then applied to that combined dataset.