Yes, you can track user interactions across multiple websites or apps with Google Analytics 4 (GA4).
GA4 allows you to create an App+Web property, which can track user interactions across multiple devices and platforms, including websites and mobile apps. This allows you to see a unified view of user behavior across all of your properties in one place.
You can use GA4’s cross-device reporting to track user interactions across multiple websites or apps, which provides you with a better understanding of how users are interacting with your properties across different devices.
Additionally, GA4 allows you to use the User ID feature, which allows you to identify users across multiple devices and sessions. This feature helps you to track user interactions across multiple websites or apps, and to see how users are engaging with your properties over time.
It is important to note that to use the User ID feature, you need to have a Google Analytics 360 subscription or a Google Workspace plan.