I checked on this option 1.
For enabling Attributes, we have to disable the “Customize Login Page” under Branding → Universal Login.
Even after enabling Attributes, while trying to change the Verification Method from Email Verification Link to OTP, its throwing a error “Error!Email verification using otp is only compatible with Identifier First.”
Identifier First option under Authentication → Authentication Profile means no Custom Login Page.
Is there a way to achieve Email Verification with OTP for applications that have custom login page.