It’s hard to say for sure without more info, but my first guess is that you’re missing the Apple Worldwide Developer Relations Certificate Authority intermediate certificate.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"
>My keychain now includes "Apple Root CA" and "Apple Root Certificate Authority".
Does that mean they're the new ones? Not expired?
If so, for the projects, involved, use Xcode's Product menu, then, with the option key pressed, select 'Clean Build Folder'. Confirm no errors in the navigator and go again.
If they are expired, follow the link eskimo provided, delete the old ones via Keychain Access first, then install the new, then do an option-clean build folder.