证书导出无法选择p12格式

Sadly, I don’t read Chinese, so I’m relying on a machine translation of your post.

I suspect that the reason why you’re not able to export a .p12 is that you have just a certificate. A .p12 usually holds a digital identity, that is, a certificate and a private key that matches the public key in that certificate.

I discuss these concepts in a lot more detail in TN3161 Inside Code Signing: Certificates.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

like that?

That popup is what you’ll see if you only have a certificate. In Keychain Access, if you select My Certificates at the top, do you still see the relevant item? If you do, try to export from there. If you don’t, it’s not showing because there’s no private key that matches the public key in your certificate.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"