Sampled data in GA4 is the aggregate data or the gross data collected by Google Analytics. If a report is sampled it means that the report is based on 100% data available. You can view a green check icon on the top that shows that the report is sampled.
Another type of report is the threshold applied or unsampled report. Such a report has a threshold applied to it. We cannot change the threshold, as it is only decided by Google Analytics 4. There is an orange triangle icon appearing on the top that shows that the report has the threshold applied to it.
So before dealing with any report, always check whether the report is sampled or not.
You can watch our video above and have a detailed look at the types of reports.