Most of GA4’s pre-built standard reports, however, are based on aggregated data. Aggregated data is the result of condensing your hit-level website traffic along certain dimensions. An example would be the sum of all sessions (aggregated metric) per channel (dimension).
These kinds of reports are not affected by the data retention settings and, therefore, will always be available for analysis. Even long date comparisons will work just fine in GA4’s standard reports.
So, why care about the data retention settings then? If you have been working with GA4 already, you might have noticed that GA4’s standard reporting is minimal compared to good old Universal Analytics. To overcome these limitations, GA4 makes wide use of the Analysis hub.
For the Analysis hub, GA4 uses fine-grained, event-level data to give you all the flexibility you need to answer specific questions. However if your data retention settings are currently two months and you want to analyze data for the last six months, you will run into a similar error like this: