I run an analytics tool called Apstal. Couple months ago I was debugging why our own signup numbers didn't match between our database and our analytics dashboard. Difference was about 12 percent.
Turned out it wasn't a bug. Adblockers were eating the analytics requests before they ever left the browser.
I got curious and checked across 13 sites that use Apstal. 108,344 events later, the number was 8.6 percent overall. On mobile it was 13.6 percent. Brave browser alone was responsible for almost half.
The thing that bothers me is not that the data is missing. It's that most people don't know it's missing. Your GA4 says 4 percent bounce rate and you feel good about yourself. Real number is closer to 68 percent.
I'm not saying this to sell anything. The free tier on Apstal is 100k events/month, I literally don't care if you sign up or not. I'm saying it because I spent months building tracking infrastructure and this was the single biggest surprise.
Also if you're wondering who uses adblockers: mostly developers, designers, and people who know what a cookie is. Exactly the audience whose behavior you'd want to understand if you're building developer tools or technical products. And you're missing all of them.
Anyway. Check your own numbers if you can. Compare server logs against what your analytics dashboard shows. You might be surprised.