To track hundreds of websites all at once with Google Analytics, you can use the Google Analytics 360 Suite, which is a paid enterprise-level solution offered by Google.
With the Google Analytics 360 Suite, you can use the "Roll-Up Reporting" feature to combine data from multiple websites into a single view. This allows you to see the aggregate data for all of your websites in one place, which can be very useful for analyzing trends and identifying patterns across your entire web presence.
To set up Roll-Up Reporting in the Google Analytics 360 Suite, you will need to create a new property for each of your websites and then create a new Roll-Up property that will collect data from all of the individual properties. You will also need to set up filters to ensure that the Roll-Up property only includes the data that you want to analyze.
If you are using the free version of Google Analytics, you can still track multiple websites, but you will need to create a separate Google Analytics account for each website and then log in to each account separately to view the data. This can be time-consuming and inefficient if you have a large number of websites to track.