When GA4 doesn’t show all your visitors, it’s usually because your tracking is “brittle.” High-security browsers (like Brave) or privacy-conscious users often block the GA4 script by default. This can lead to a 20% or even 40% undercount of your actual traffic.

To solve this, you need to “harden” your tracking. Using a first-party server-side setup makes your tracking look like a natural part of your website’s heartbeat. This allows the data to pass through most blockers, ensuring that when you look at your GA4 dashboard, you are seeing the real number of people visiting your site, not just a filtered version of it.