During the process of generating the .p12 file for the prepared certificate file, the .p12 option was grayed out and could not be selected and exported.
Solution
At first, I thought there was something wrong with the generated blank CertificateSigningRequest. I tried making it several times but it didn't work.
Then I found that the problem was with the keychain access options...
Switch the top menu tab from "All Options" to "Certificate" The .p12 file can be generated normally...
as shown in the figure below...
The above is all the content shared this time, I hope it can be helpful to everyone!