https://www.theregister.com/2020/06/02/sectigo_root_cert_expires/
My browser is fairly up-to-date so it used the new chain. You'll have go the manual install route if Apple doesn't issue a root cert update for the older Safaris.
On Saturday, at 10:48 UTC, Sectigo's AddTrust legacy root certificate expired, causing a bit of weekend havoc for thousands of websites and services that rely on it for making a secure TLS/SSL connection.
My browser is fairly up-to-date so it used the new chain. You'll have go the manual install route if Apple doesn't issue a root cert update for the older Safaris.