https://arstechnica.com/gadgets/2020/11/mac-certificate-check-stokes-fears-apple-logs-every-app-you-run/

Last Thursday afternoon, Mac users everywhere began complaining of a crippling slowdown when opening apps. The cause: online certificate checks Apple performs each time a user opens an app not downloaded from the App Store. The mass upgrade to Big Sur, it seems, caused the Apple servers responsible for these checks to slow to a crawl.

Apple quickly fixed the slowdown, but concerns about paralyzed Macs were soon replaced by an even bigger worry—the vast amount of personal data Apple, and possibly others, can glean from Macs performing certificate checks each time a user opens an app that didn’t come from the App Store.