You can exclude all data for a project from being used to personalize ads, and thus reserve that data for measurement purposes and content personalization (e.g., A/B testing).
If you exclude project data from ads personalization, then any audience that is based on that data is not eligible for export from Analytics for Firebase to any of Google's advertising products (e.g., Google Ads, Display & Video 360, Search Ads 360). This also applies to any audience whose component audiences are based on that excluded data.
That data and any audiences based on that data are still available within Analytics for Firebase for use in reports and audience building, and can be exported to non-advertising products like Optimize and BigQuery.
To manage how project data is used to personalize ads, sign in to the linked Analytics account and follow the instructions for using the controls in Analytics Admin.
Other ads-personalization controls
If you want to disable ads personalization for a single event or user property, and not for all events in a project, then there are other controls you may want to consider: