So what was the cause? It appears a server problem at Apple was the culprit. Macs regularly check in with Apple's servers to check the validity of certificates. When a user is offline, notarization validation is supposed to "soft fail". This means the operating system will launch the app anyway.
In this case, the process malfunctioned as devices could perform a DNS lookup on Apple's Online Certificate Status Protocol service but failed to connect to the service. This resulted in time-outs rather than "soft fails", resulting in odd behaviour in the operating system.
It didn't take long for some Mac users to note that trustd—a macOS process responsible for checking with Apple's servers to confirm that an app is notarized—was attempting to contact a host named oscp.apple.com but failing repeatedly. This resulted in systemwide slowdowns as apps attempted to launch, among other things.The problems started around the time Apple started the rollout of Big Sur. Fortunately, the issues didn't last long.