Intuit Link has its problems but if you use it as your client portal, there's little reason for you to share the return with your client by alternative means.  If I were you, I would cajole my clients to access the return on Intuit Link especially since there is really no downside to this so long as you use the "Act as taxpayer" function to upload the return rather than sharing the return with client via PTO.

Since we no longer use Intuit Link, we use our secure client portal to share returns (and exchange tax data/documents with clients).  We also use encrypted emails (which our clients can access via a portal) as an alternative means of communication.

In case you don't have access to encrypted emails, sending the return over email should only be done if you use a PDF editor to password protected the file for at least read access or you can simply password protect it with a ZIP utility.  I would also send the password separately from the email with attachment.