non-www to www

So, my site is listed in general settings as https://www.mysite.com. BUT if I go to any page like https://www.mysite.com/about, and then remove www from the url (ie: https://mysite.com/about) and hit enter, https://mysite.com/about loads.

On other WordPress sites, typing in https://mysite.com/about would redirect the user to https://www.mysite.com/about/

I can’t figure out what I’ve done wrong and how to fix this?

I use Yoast? Is there a settings issue that causes this?

I ask because I’m running reports on missing page titles, alt images and all of the errors point to https://www.mysite.com pages specifically. It’s strange because they shouldn’t be appearing as their own pages since the site is officially listed with www.