SECTIGO CPAC Pro S/MIME certificate is displayed as not trusted in macOS Keychain.
Cause: The intermediate certificate Sectigo Public Email Protection CA R36 for ECC-based keys is missing.
Solution: Install the Sectigo Public Email Protection CA R36 certificate - Download: https://crt.sh/?d=4267304694
For more information from SECTIGO / Source:
https://www.sectigo.com/knowledge-base/detail/Sectigo-Public-Root-CAs-Migration/kA0Uj0000003RoT