eDiscovery for email attachment with encrypted sensitivity labels

Thanks. We do have the eDiscovery Premium license, which enables us to search encrypted content in OneDrive, SharePoint, and email including attachments (as long as the document was unencrypted at the time it was attached, and the entire email was subsequently encrypted). However, we’re unable to search encrypted email attachments (if the document was encrypted by label and then attaches it to an email message), regardless of whether the email message itself is encrypted or not. In the link, it mentioned:

• Attachments encrypted separately from an email can be decrypted if the attachments are Microsoft 365 documents. For example, if a user encrypts a Word document and then attaches it to an email message that isn't encrypted, this attachment is decrypted.
• Attachments encrypted as part of the encryption of the associated email message are decrypted. For example, if a user creates an email message, attaches an unencrypted Word document, and then encrypts the message (including the attachment), this attachment is decrypted.

The second bullet works, but not the first bullet. We are in GCC. Just want to know if it is an expected behavior or there is some setting, we need to turn on.