Many Mac users experienced app slowdowns during the launch of Big Sur, possibly due to issues with Apple's OCSP service being unable to validate certificates (Ars Technica)

Ars Technica:
Many Mac users experienced app slowdowns during the launch of Big Sur, possibly due to issues with Apple's OCSP service being unable to validate certificates  —  Even Macs that didn't upgrade to Big Sur had problems.  —  Mac users today began experiencing unexpected issues …