It's not so much that they'll leave, as much as some percentage will abandon during the signup flow. I know somewhere out there are statistics on those who have

It's not so much that they'll leave, as much as some percentage will abandon during the signup flow. I know somewhere out there are statistics on those who have to click a link in an email only to get distracted by other emails, to say nothing of the time to fill out forms, create a password, save to password manager, open your 2FA app for the more advanced users, etc.