A library in Google Analytics 4 collects all of your reports and their data in one place. The library displays the names and brief information about your all reports. You simply have to click on any reports to get further details.
Step 1: In the left menu, go to the reports
Step 2: In the reports bar, click on the “Library”
Your library will appear showing all of your customized reports. You can see every type of report you have generated or customized.
Moreover, the library shows details of the reports, like who created the reports, the dates modified, and other descriptions.
Click to watch video on How to Customize GA4 Reports?