Except for the fact that if your e-mails are encrypted, you can’t search them in Apple Mail.

This seems more like a problem in Apple Mail than SMIME

Indeed. The client could maintain a vector search table that contains "unencrypted" data from emails, but the table itself could be separately encrypted on-device to the same level of security as the rest of the iPhone/MacBook/etc (T2/TPM/HSM chip). Definitely a client problem.

Oh, yes. I never claimed otherwise. But if you’re a user of Apple Mail and are looking for a solution for encrypted mails today, you should be aware of this.

They have the opportunity to make PGP completely seamless.