I want to track the overall crash rate of my app.

In order to get crash rates for your apps, you need to set up releases. This will make Sentry start tracking release health through sessions, and therefore start tracking crashes through a crash free session rate and a crash free user rate. Please see how to set up releases for your chosen SDK here.

These rates will be available as a per-release statistic in your Releases tab. For a more personalised view based on what you need to track, you can set up Dashboards (Business or Enterprise Plan for SaaS customers).