Can't send mail from alias email addresses since upgrading to macOS Tahoe

Just updated to macOS Tahoe. I receive emails TO my various icloud aliases without a problem. However when I want to respond to those emails, the send FROM email defaults to my primary email account, not the alias to which the email was sent.

Since the entire point of having an alias is to keep private your main email address, and thus it would entirely defeat the purpose of having an alias to not allow sending email from it, I am assuming there is some option or setting I need to set somewhere?