There is no such thing as secure or private email or text messaging unless you and I both take take special precautions, such as by using the same encryption program (such as Signal). Otherwise service providers like Gmail are free to use the contents of your messages for marketing (such as to send you advertisements).
For example, if you start a conversation by text or email and mention anything personal, it’s no longer private (even before I receive it). Consider something as simple as the following:
Dear Dr. Turnbull:
I have been suffering from depression and mild anxiety for the past several months. I used to take anti-anxiety medication but I feel like I need to get back into therapy and figure out how I can try and solve this better than I have in the past. Do you have any appointments available?
From this alone, you may start to receive ads for anxiety medication or treatment centers as you continue to browse the Internet. If I answer and include your message in the reply, I have just violated federal laws and regulations (HIPAA) that are designed to protect the privacy of your Protected Health Information. So . . . do not include confidential or private information regarding your health in email or text messages.
Perhaps you would rather just call me?