How to design for preferences when optional and mandatory options are both available?

I saw an unexpected sign up process with the Ghostbrowser beta invite when creating an account, and I wondered what the conventional strategy is when you have to mix mandatory and optional choices on the same interaction/page?

To me it is a little bit confusing at first because the section itself is mandatory, but the selections are checkboxes which implies that you don't have to make specific selections. However, if there are options which are required and errors are generated if you don't select it, then why even bother asking the user to select it?

See the screenshot captured below:

How can these types of mandatory + optional selections on sign up preferences be managed in a more graceful manner?