Nosing around the macOS 13.0 sources I stumbled across a comment regarding Mac Office 2008 in the security_certificates source drop.
# M I C R O S O F T H A C K !
# It turns out that the Mac Office (2008) rolled their own solution to roots.
# The X509Anchors file used to hold the roots in old versions of OSX. This was
# an implementation detail and was NOT part of the API set. Unfortunately,
# Microsoft used the keychain directly instead of using the supplied APIs. When
# the X509Anchors file was removed, it broke Mac Office. So this file is now
# supplied to keep Office from breaking. It is NEVER updated and there is no
# code to update this file. We REALLY should see if this is still necessary
Wasn’t Office 2008 a 32-bit app, in which case it would’ve stopped working long ago when they dropped 32-bit support from the operating system?