Because we can't have nice things, Apple has to check that apps are signed with a current certificate for safety and security reasons. OCSP tells the client if the certificate has been revoked or not.
Try opening a non-https web page; you'll get a bunch of ominous warnings from all major browsers.
Browser certificates need to be OSCP signed for the browser to trust them. You can't even get a new cert if the issuer’s OCSP server goes down, which does happen on occasion.
There are so many dependencies to ensure we're not running malware infected apps that sometimes things break.
Let’s not get carried away; every major tech company has had some version of this happen at one time or another.
FWIW, I haven't experienced any issues with my iMac running Big Sur running Apple or 3rd party apps all day.