On September 13th, 2021, a critical security flaw was fixed in both 10.15.x (Catalina) and 11.x (Big Sur).
Based on issues people have exprienced going from Catalina straight to Big Sur, we're recommending people currently running 10.15.x only run the security updates and not upgrade to Big Sur.
From the Apple Menu, choose "About This Mac." You'll see a screen similar to below. Note the version you're running.
Click "Software Update."
If you are running 11.x (Big Sur), please run any updates available. As of this writing, it should be an upgrade to 11.6.
If you are running 10.15.x, your screen will look similar to the one below. Do not click "upgrade now." Rather, choose the diminutive "More info..." link toward the bottom left.
Make sure all updates are checked and click "Install Now."
