Yes, we provide the SSL certificate through the subdomain when it is added in your account’s settings. This ensures that the "www" traffic is secured.
beehiiv does not directly secure root domain traffic, however, you can try adding this A-record with your DNS provider (not all providers will accept it). After adding the A-record, root domain traffic would also be secured.
Note: 301 or 302 redirects would not secure traffic from root domains.